Can I share a bore?
Certainly. If one or more neighbour’s have their own existing independent reticulation system we can drill one bore and have it connected into each neighbour with independent operation from each reticulation controller. Shared bores are quite common in Perth. Often neighbours choose to draw up a simple shared bore agreements. We have examples we can share with you.
How long does it take to install a new bore?
Generally about a week from start to finish. A day to drill, case and gravel pack the borehole then air develop or flush the borehole. Another day for the stainless steel submersible pump installation. Then the bore electrician attends to connect to mains power and link to the reticulation controller for auto starting if required. Finally connection to retic system if part of scope of work and handover to client. Our workload is quite seasonal ao the ideal time to have a bore drilled is before Perth summer gets in to full swing.
Do Perth metropolitan garden bores require a groundwater licence?
Short answer: NO. The following excerpt is from WA Government Department of Water Website.
“Domestic garden bore users in the metropolitan area do not require a licence. They have been exempted from the requirement to have a licence through an Exemption Order under the Rights in Water and Irrigation Act 1914.”
We have answered more questions on Perth water bore licensing and permits here along with links to relevant info at the Department of Water.
Are there access restrictions determining where I can have my bore drilled?
It surely brings a smile to our faces when we can back a drilling rig up on a nice flat front lawn but we understand that this isn’t always possible. We have smaller rigs for tight spots, 4WD drive drilling rigs for difficult terrain and even track mounted rigs often available for when the going gets really tough in sloping sandy sites. Sometimes the only location to drill is in the driveway with the borehead nicely finished of with a trafficable lid. It is best if the position selected is as close as practical to the proposed electrical power connection. Of course we also have to avoid underground services such as Telstra, gas, water and sewerage. We must also be clear of overhead obstructions.
How do I pay?
See details under “contact us” tab or for Visa and MasterCard credit card payments click here.
EFT details are at the bottom of your Virgin Bores invoice if you wish to pay online.
Yes, commonly we connect new bores in to existing sprinkler systems that previously used mains supply water. Most Perth bores are connected to irrigation or reticulation systems. Details on how a bore is connected to an existing home reticulation or irrigation system can be found in this article.
How is a new bore connected to my reticulation system?
Put simply the pipe from the new bore is connected in to the main water line of your existing reticulation system. The existing reticulation system is disconnected from mains water where it is fed from, normally near the water meter. Your existing reticulation controller is then wired to send a 24v start signal to the new bore start box. We normally do this for most new bore installations as a “turn key” solution. Far greater detail is explored here in this article on our website.
Won’t the extra pressure blow up my sprinklers?
Typically a new bore for a home would be configured to give up to double the flow that was delivered by the mains water supply. If being connected to an existing reticulation system we can accommodate extra flow by doubling retic stations to come on together if required.
Give us a call or email a service request. It would be helpful for us to know firstly ” Is it an old well – style with concrete well liners and a tin lid where you can see the pump underneath? ” or ” is it a modern submersible style where nothing, except perhaps an A4 sized access lid is visible”. If it is the first ” old well style” it would help us if you could tell us if the pump is starting but no water or if the pump is not starting at all. This helps us send the correct service personnel first time and helps avoid multiple call-outs.
Should I test my bore and reticulation during the Perth winter sprinkler bans (1st June to 31st August) and am I allowed to?
Yes and yes! It is very wise to run your system briefly at least once a fortnight. Particularly with centrifugal pumps in wells as the check valve may be susceptible to a slow leak and prime could be lost if not started regularly. It is not as important with submersible pumps but none-the-less wise, as it ensures everything remains “free” to turn and also that reticulation system solenoid valves (and their diaphragms) operate. The following is extracted from the WA Gov’t Department of Water guidelines on their website:
“Can I maintain my bore during the winter sprinkler ban ?“ Maintenance of garden bores is important and under the legislation a person does not commit an offence if the person operates a reticulation system using domestic bore water to the minimum extent necessary while the system is being installed, maintained, tested and repaired.
The minimum extent necessary is considered to involve limiting testing to a maximum of 2 minutes per station. Running your reticulation longer than this may be deemed as watering your garden.
The Department recommends that wherever possible maintenance, repairs and testing are carried out on one of your allocated September to May sprinkler roster days (where applicable) and before 9 am or after 6pm“
That is a bore electrical problem of some sort or a fused motor. Firstly we would recommend we send a bore specialist electrician to repair if simple or certify motor as fused ( possibly giving rise to an insurance fusion claim).
Are all Perth suburbs OK for a bore?
Most Perth metro suburbs are suitable. Give us a call on Perth 1300 734 300 or email us and we can confirm status of your particular property based on our extensive Perth metro experience and using the data available from the Perth Groundwater Atlas.
It depends on the depth to water at your property. Depth to water is partly related to how high you are above sea level so high on a hill generally costs more and down low generally costs less. Call or email us, we can tell you the price quite accurately,without even visiting site by accessing the data on the Perth Groundwater Atlas. Roughly though, water bores in Perth range in price from $2800 to $7000 as a finished project. Most Perth bores are at the lower end of this price range between $3,000 and $4,500. Differences in water bore cost include pump size and type, depth to water, and access considerations. Ask for a bore quote here? or call 9246 0111 and we can even give you an indicative bore price over the phone. Perth 7 days.
Sure you can. As long as it is a typical retic controller that operates solenoid valves then yes. More than 99% of old controllers have a master valve output for your master solenoid valve or they have a pump start output. Either of these will start the pump via a 24v relay. Easily done. Some clients take the opportunity to upgrade their old reticulation controller whilst the electrician is there wiring up their new bore pump. There are even new wi fi enable retic controllers that can be operated from your smartphone. Check out our article on the new internet enabled Hydrawise retic controller here.
What does it cost to run a bore?
Most new bores installed in the last 20 years in Perth have modern submersible pumps where the motors are 1.1Kw (1.5hp) or if a deeper bore a 1.5Kw (2hp). The cost to run them is therefore minimal. A 1.1Kw (1100 watts) motor uses 1.1Kw of electricity per hour. Check your Synergy bill for your current cost per Kw.
Often with restricted access sites we drill the bore in the driveway. The roughly A4 sized access lid can be paved over. If it is a concrete or liquid limestone driveway a trafficable lid can be mounted level with the surface or a cut-out of the existing surface can often be made to go over the bore lid.
How much room does a submersible bore take up?
Shown here is a Nedlands bore just drilled. It has not yet been connected to either electrical (orange circular cable) or to the reticulation system (via 40mm black poly rising main). Note the stainless steel cable that suspends the submersible pump at the bottom of the bore hole. The actual borecasing is the 100mm white class 9 PVC. Over this will go a bore box which can be positioned under lawn, paving, garden or level with the surface if required. The footprint of the borebox is commonly about 400mm x 300mm. The picture above right under paving is an example.
Not currently (as at August 2012) and no talk of reintroduction.
I have a submersible bore. The box on the wall says” Lowara” and the switch keeps flicking off. It’s about 15 years old. Can you fix it?
Yes we can. It may be the switch itself faulty or a symptom of some other problem such as the start capacitor. Our bore specialist electrician will fix it. Call us on 9246 0111 for all bore repairs or book a bore service here.
I have a submersible bore that’s quite old and I don’t know the brand of the pump. I think it may be “Grundfos” but am not sure. Can you fix it?
Most submersible pumps and motors that are in domestic bores in Perth are whats called 4″ pumps. We repair or replace all brands and can supply any brand available. Note however, most 4″ pumps and motors are all interchangeable.
There are some known spots identified in the Perth Groundwater Atlas that present potential salinity concerns. Virgin Bores can advise on this. See also Dept Water under our “useful info” tab.
Are there any Gov’t fees or charges for garden bores in Perth?
No. Reference August 2011 Dep’t of Water Operational guidelines 5.17- excerpt- “Are there any fees or charges for metropolitan garden bores? There are no fees or charges payable to the department for allowing construction or use of a garden bore.”
Quite often yes. It is always wise though to have the water tested first. Simple tests can be carried out by your pool shop or more comprehensive analysis by special testing laboratories. Hardness and pH need to be considered amongst other factors.
Many clients without access to mains scheme water drink bore water. It is most important though to have it tested regularly by an accredited laboratory to ensure suitability for drinking.
Sure, we frequently connect standard taps or gate valves on stand-pipes to run off bores. Typically if being connected into an existing irrigation or reticulation system we would plumb in the bore tap before the solenoid valves. This delivers bore water to that tap outlet whenever the pump is running. We would normally wire the reticulation controller so the bore tap could then also deliver water whenever any reticulation station was running. This also allows the bore tap to be run by itself, but we caution
that the tap must only be used solo with it fully opened and coupled to at least a 3/4″ hose ( not standard 1/2 ” garden hose) when used by itself. The hose should also have no restricting device or nozzle on the end. When installing manually operated taps to water bores we normally recommend fitting a pressure release valve at the same time.
What is a Pressure Release Valve?
This is a safeguard against “dead-heading” of the bore pump. The pressure release valve is designed to open and release the water if the pump is accidentally started with the tap closed and nowhere for the water to flow/escape. Similarly if solenoid valves in a water bore reticulation / irrigation system failed to open whilst a pump is running the Pressure Release Valve allows the water to escape and helps prevent consequential damage.Pressure Release Valves are either preset or calibrated and adjustable. They are sometimes also referred to as pressure relief valves. It is important that submersible pumps are not run whilst the water flow is overly restricted or shut off (dead-headed) as a likely consequence is overheating of the pump motor, in turn causing the rising poly main (water delivery pipe) coming up from the pump to get hot and malleable with the water pressure build up sometimes blowing a hole in the side of the softened pipe.
Like everything, yes there is some relationship. There are some very cheap imported pumps that we simply won’t touch. Bargains too good to be true most often aren’t. It’s not sensible to compromise on quality and sacrifice reliability particularly when it comes to pumps installed underground. On the other hand there is no point in paying too much. An experienced, licensed, water bore driller with local knowledge will be able to ensure the right products are used in the construction of your bore to the required standards. A large local company like Virgin Bores are also in a position to pass on the savings from economy of scale and bulk purchasing power. We go to great lengths to protect our good name!
How much does a water bore cost?
It mainly depends on the depth to water at your house which in turn is related to how high above sea level you are. Call us on 9246 0111 and we can look up the depth to water and give you a price. Or ask for a bore quote online here.
It varies by brand. Most stainless steel submersible pumps and motors that we deal with come with a two year manufacturers’ warranty. Centrifugal pumps for wells commonly have a one year manufacturers’ warranty.
Unfortunately I live in one of the Perth suburbs where bore water stains. What can I do?
Firstly we can design / modify reticulation sprinkler systems so they do not spray water on areas of concern. A combination of drippers, micro sprays, shrubblers and even sub-surface irrigation can be used. Bore stain can be removed using proprietary cleaning solutions or call us if you wish to unload this task onto us. There are filter systems designed to handle iron oxide staining. These are handled by specialist companies to which we are happy to refer you. Finally, remember that staining is aggravated by too much aeration of the water causing oxidation. Sprinklers must not be run under too much pressure. Often we ” double up ” stations so more than one station comes on at once to alleviate this. This article Iron Bore Staining Perth published by the Department of Water has a lot more information about rust coloured iron staining and related iron oxide bacteria. It also covers black staining associated with manganese and soil carbon.
Firstly check it is still plugged in/power turned on. Try another appliance in same power point. If it is direct wired ( hard-wired) check that no circuit-breaker in meter box has tripped. Check fuse in controller. No luck? Give us a call and we will send a serviceman. Also our “useful info” page has guides for some reticulation controllers which have a troubleshooting page.
First check that you have not enabled the “rain” or “pause” function. If connected to a bore make sure any over-ride switch is not off and that no circuit breaker has tripped. If connected to mains water check that any isolating gate valve is not turned off. If you need further help please call us.
I have got an old well style bore and the pump runs but no water comes out anywhere?
Firstly, please make sure you don’t run it without water as it may cause consequential damage. Most likely it is a “priming” issue. There could be a leak below the pump or perhaps the check valve needs replacing. More seriously it can sometimes be the pipe or spear down to the water table is letting in air. Sometimes it is not a problem with the bore but instead is reticulation solenoid valves not opening so nowhere for the water to go.
I’ve got water bubbling up out of my front lawn whenever the retic is running no matter what section is turned on?
Sounds like a broken pipe in your reticulation system in one of the main lines ( i.e. a pipe before the valves)
It is not an option on my reticulation controller to program it for the individual rostered watering days that are published by Water Corp. What do I do?
Some controllers are only programmable for intervals e.g. every third day,y and this is not compatible with the individual days that are given Perth householders on the watering roster. Unfortunately you will need to have your reticulation controller replaced. Our servicemen can do this anywhere Perth metro.
I assume it is running but no bore water. Sometimes if it has not been run for a few weeks it loses prime through a slow leak and often it just needs priming. There is usually priming point on top of the pump. If it is a more serious leak it will need fixing. It might be the check valve that needs replacing. It could be leaking gland packing or even a leaking mechanical seal. Sometimes it is the ” bottom prime” i.e. the water under the check valve in the pipe that goes down to the water table has escaped. Call us, we will ask a few questions and give you some options. 1300 734 300
I have a new submersible bore in Winthrop that stains slightly. My old bore was a well-liner type in Willetton. Does the different type make a difference to the quality of the bore water?
In a nutshell no. What is in the ground beneath you and from where the water draws in the superficial aquifer is the reason. Different suburbs, different streets and even different water bores in the same street constructed to the same specifications can vary markedly and produce different bore water samples. Also a sprinkler system delivering the same bore water under too much pressure will mist and oxygenate the water more. Iron Oxide then becomes more of a problem. Experienced water bore installers will know to join stations together on existing retic, if necessary, to accommodate the extra flow of bore water versus mains scheme water. The Department of Water have published more info on bore staining in Perth water bores in this article Iron Bore Staining Perth
I’m currently building a new house in Canning Vale. What is a water bore likely to cost me?
Probably about $3500 with a top quality stainless steel submersible pump all “done and dusted ” (2017 price). Unless you’re up on the hill south of South St / Ranford Rd in which case allow more.
The drilling or “water boring” of most Perth bores is completed in a day. Some elevated positions like near the water towers in City Beach and Kardinya require quite deep bores and consequently the drilling may spread over a couple of days. Pump installation and fit-off normally another half day. Then a licensed electrical contractor is engaged to do the surface connection to house power.
There are a variety of reasons this can happen. Older reticulation controllers often contain a small glass fuse. Most commonly when the fuse blows it is it is caused by a field wiring problem in the cables going to the reticulation system solenoid valves. It may be the solenoid coil itself causing the fuse to blow. Sometimes if the system is connected to a bore it may be the 24 volt relay causing the problem. The advice reprinted below is provided by Rainbird but is applicable to many reticulation controllers.
“Rain Bird’s older controllers contain a glass fuse that is designed to blow in order to protect your timer from being damaged. Fuses can appear to look fine with the naked eye; often misleading people into thinking their fuse is good. It is recommended that you test your fuse using a volt/ohm meter. All good fuses should read 0 ohms (depending on what the meter reads when the leads are held together) and a bad fuse will read the same as holding the leads in the air.
Other procedures may be required in order to find the root cause of why your fuse initially blew. Simply replacing your fuse may not resolve your issue and might result in a blown fuse again. Follow the below procedures if the fuse is determined to be bad. Please note that permanent damage can be made to your controller if you fail to install the proper size fuse.
Step 2 : Locate your “COM” terminal and disconnect your common wire.
Step 3 : Making sure you have the correct size, reinstall your new fuse (a spare fuse is located on the back cover/panel). If your fuse blows immediately, you should test the resistance on your transformer. An infinite reading indicates that you have a bad transformer and it must be replaced. If your fuse does not blow, proceed to step 4
Step 4 : Reconnect your common wire into the “COM” terminal.
Step 5 : Turn your dial back to the AUTO position. If your fuse blows, the problem is within your controller and it must be replaced. If your fuse does not below immediately, manually start your first station. If after one minute your fuse does not blow, continue to advance through each station (allowing 1 minute of run time before advancing to the next). If you have a short within your wiring or a bad solenoid, your fuse will blow whenever your timer gets to that station. You will need to correct the problem on that station and replace your fuse again.”
Sprinkler systems should preferably be programmed to irrigate early in the morning on your nominated watering days. Early morning is the most efficient time to water in the Perth climate because water can reach its destination without being evaporated by the sun or blown away by the wind. Early morning watering also helps prevent disease and fungus caused by water sitting on plants overnight. It can also help avoid undue compaction caused by heavy traffic on wet ground. When thinking about the best time to water on any Perth property consideration should also be given to local wind times and patterns.
Different brands and types of sprinklers have different precipitation rates. Take a look at our article on this here which references Water Corp’s handy guideline.
What does a Perth reticulation system cost ?
For a pretty standard Perth block of say 500 sq metres with an average new house the proposed garden/ lawn areas would generally cost about $3000 to irrigate professionally. Reticulation often costs more in established gardens as they are usually more complicated to retrofit once paving lawn and gardens are already in. Send us a rough sketch or landscaping plans of your garden and we will give you a closer estimate or quote. Or call us on 1300 734 300. We will meet onsite to give a quote for reticulation, Perth and all metro suburbs. More Perth reticulation info can be found here.
Help! How do I find my solenoid valves?
Solenoid valves are the 24 volt device, normally underground, that allow an automatic reticulation system to change from one station (group of sprinklers) to another automatically. If a solenoid valve is broken it may fail to open or sometimes it gets stuck on. Easy to fix if the location of the valve is known. If not a special cable locator or cable tracing wand may be required. Our Perth service team can help locate lost solenoid valves 1300 734 300 and trace broken solenoid wires.
At my last house we turned the bore on and off from a simple switch and I changed the sprinklers to do front then rear by manually turning two gate valves. This time you are connecting it in to my auto sprinkler system. How will it work?
Your automatic reticulation controller currently tells a master solenoid valve to open allowing mains water from the street at the same time it opens each individual solenoid valve to operate each station (section) of your retic. Instead ,when connected to a bore, the 24 volt signal from your retic controller that was opening the master solenoid valve will instead be redirected to a relay or contactor which will turn on the 240V bore (or 415V if 3 phase). There will no longer be any need for a master solenoid valve as there will be no constant pressure against the individual solenoids unless the pump is turned on. Some solenoid valves may be doubled up so two or more stations open at once to allow for the extra flow from the bore.
What is a rain sensor?
A rain sensor, such as the Rainbird RSD pictured, is a device that connects to your reticulation controller to turn off your sprinkler system when it rains. Rain sensors can turn off irrigation that runs from a bore or mains scheme water. There are rain sensors that are suitable to connect to almost all types of reticulation sytems. Some are hardwired 24 volt and some are wireless.
Generally speaking it is a pump that is designed to be submersed under water. Modern submersible pumps are normally made from stainless steel and are commonly cylindrical. Normally they are two parts bolted together. The “wet-end” or pump which contains the impellors is the top part and the single or three phase electric submersible motor is beneath that. The motor has an electrical lead which is heatshrunk making a waterproof connection to the power cable leading up through the water and to mains power. Perth garden bores usually have the pump installed in a 100mm diameter borecasing with the pump hung on a stainless steel cable 6 to 12 metres under water.Water is delivered through a rising main to the surface which in Perth garden bores is normally 40mm rural poly pipe.This is then connected to a tap or garden reticulation sprinkler system
If a bore is constructed properly it is a fairly simple procedure to retrieve the pump. Perth bores range in total depth from about 12 metres in low lying areas to over 80 metres at high points such as near the water tower in City Beach or elevated positions such as seen in parts of Kardinya and Sinagra. Very shallow bores can sometimes be pulled by hand. With most deeper bores we commonly attach a purpose built winch to the stainless steel draw-wire that is fitted to properly designed bores at time of construction. Whilst carefully pulling by hand on the electrical cable and rising main (normally 40mm rural poly pipe) the winch connected to the stainless steel draw-wire slowly draws the pump and motor to the surface.
Standing or Static Water Level (SWL) is the level when a bore is not being pumped. Commonly bore water draw down refers to the level the water falls to bellow SWL upon pumping. Natural draw-down in cased bores may also occur due to seasonal or climatic change. Excessive draw-down leads to bore yield issues.
What is air-development or air-developing?
In relation to the installation of new water bores it is the process whereby after water bore drilling , casing and gravel packing the new borehole, and before the installation of the pump, compressed air is pumped down the inside of the bore-casing to clean the screens or slotted casing and encourage water flow. It develops the recharge rate of the bore.
In relation to old bores where there is excessive draw down and the groundwater recharge or flow may have diminished over time, due to clays etc, the existing pump is temporarily removed and air developing is carried out to rejuvenate a ” tired” bore”. Sometimes air developing rejuvenation of old bores is done in conjunction with chemical development where the bore is dosed certain cleaning compounds, surfactants and clay dispersants . Sometimes chemical development alone is called for. Call us on 9246 0111 for advice.
We can assess the problem and probably rejuvenate your “tired” old bore with the treatments above. Sometimes treatment to redevelop the bore is not enough and the yield of water flowing in to the bore is not quite enough to power the existing reticulation configuration or sprinklers properly. In this case to get the water flowing out to match the water flowing in, the reticulation system can be reconfigured, often using “low precipitation” sprinklers and the output pipe restricted with a gate valve.
If you find that a certain station (sometimes called a zone, section or group of sprinklers) of your reticulation system comes on regardless of which station is turned on then it is almost always a faulty or dirty solenoid valve (pic of solenoid valve sectional view to left) that needs replacing or cleaning. A tell-tale sign of which solenoid valve is sticking open (lets assume it is station 2) is that when you run station 2 everything appears normal, but when any other station is turned on then station 2 comes on as well. The station that appears to function normally is in fact the one that needs repairing!
Visit Water Corp’s ” Rostered Perth Watering Days” page. There is a link on our ” useful info ” page. Watering days in Perth include a bonus 3rd day for Perth bore users. Perth watering days are designated by the last digit of your street number. The three day watering roster for garden bore owners works on the same roster as two day a week scheme water users, plus an additional day.The daytime sprinkler ban between 9 am and 6 pm for bore owners remains.
Are all areas of Perth suitable for a water bore?
No. In some Perth foothills areas, particularly where there are clay soils bore yields and flow can be limited. Some areas close to the Swan River estuary or the ocean can be subject to saltwater intrusion particularly if over pumped. Drilling of water bores in the immediate vicinity of some wetlands is discouraged. Virgin Bores can advise on suitability in your area. Please give us a call on 1300 734 300. Info on groundwater suitability is also available in the “Perth Groundwater Atlas”. A link to the Atlas is on our useful info page.
What areas do you cover?
We regularly drill new water bores all over the Perth greater metropolitan area from Lancelin in the north down to Mandurah in the south and all suburbs in between. We are also one of a select few water bore companies that regularly undertake drilling deep bores in semi rural areas such as Woodridge and Gabbadah where the water source required for the rotary mud drilling process may not be readily available.
Random but interesting input:
Dec 7, 1895 – On his return to Perth on 7 December 1895, Forrest pledged to” increase the number of goldfields electorates to five; to authorize many new water bores on the Eastern Goldfields, including one of 3000 feet in depth to search for artesian water; and to construct a network of new rail lines from Coolgardie to the main centres.” Two days later, the first steamer to do so discharged its cargo in the new Fremantle river-mouth harbour.
Will my bore stain?
Rust coloured bore staining does occur in some Perth suburbs. The “Perth Groundwater Atlas” published by the Department of Water indicates areas of likely bore water staining. Iron staining is more commonly found close to present or old (past) wetlands.
Call Virgin Bores on 1300 734 300 and we can advise on known staining issues in your suburb and street.
If there is an assessed bore staining risk at your property Virgin Bores can advise on strategies to minimize the cause and effect.
What causes bore staining?
There are several types of staining but most is commonly that referred to as “iron staining”. The following partial extract from a 2006 Western Australian Government Department of Water paper gives a scientific explanation of bore stain associated with iron-rich groundwater:
“Iron is the metal that is most abundant on Earth and is therefore very prevalent in soils and
groundwater. Dissolved iron occurs naturally in groundwater in concentrations of up to around 50
milligrams per litre. Iron salts become increasingly soluble as groundwater becomes more acidic.
In anoxic and acidic groundwater (pH values below 5), iron concentrations of one to 20 milligrams
per litre are common (usually as stable carbonates). Iron is normally found dissolved in
groundwater in the reduced ferrous form (Fe2+)and oxidises to relatively insoluble ferric form (Fe3+)
when the water pH is raised and with exposure to oxygen in the air.
When acidic iron-rich groundwater is extracted and mixes with air, carbon dioxide and hydrogen
sulphide (rotten egg gas) is frequently released, the pH rises and the iron precipitates as ferric
hydroxide (rust) on any flat surface where it rests as water evaporates. Over time this oxide coating
builds up causing discolouration to light coloured surfaces.
Iron may also be present in groundwater in organic complex and slimy, but harmless, bacterial
forms. These are unlikely to settle out, but may discolour water.”