Managing your private water supply

Tips on managing your water supply to keep it safe including types of contamination, maintaining different sorts of filtration, UV systems and pH correction.

There are many things you can do to keep your water supply safe. Contamination from a variety of sources can occur potentially at any point throughout a water supply system if it is not robust and adequately protected. The more protection provided to the source of a water supply, the less strain a treatment system is likely to be under which may reduce overhead costs in the long-term.

The guidance below includes:

Types of contamination

There are two broad categories of contamination that can affect the source of a private water supply:


Surface derived sources such as springs, wells, streams and lakes are highly susceptible to bacteria contamination. Faecal matter from animals is a particular concern and contributes to most ill-health issues. These pathogens present a danger to young children, the elderly and those with compromised immune systems for example those receiving chemotherapy.

We routinely test for pathogens such as:

  • E. Coli
  • Enterococci
  • Coliforms
  • Clostridium
  • Pseudomonas

We don’t test for pathogens such as cryptosporidium directly, however the presence of other pathogens listed above indicate potential for their presence.

In all cases, the greater the separation you can make between your water source, animals and faecal matter and septic tanks, the lower the risk your supply will be contaminated.


There are many different kinds of chemicals that can enter into water supplies and good planning should be undertaken to ensure responsible chemical applications.

Pesticides and fertilisers used in agricultural settings are prone to being washed into water courses following rainfall. Pesticides should be used far away from water sources with particular attention to timing of deployment. Using pesticides prior to heavy rain runs the risk of polluting water courses and wasting your investment.

Fuel and solvent pollution can ruin the wholesomeness of a water source and compromise tanks and treatment systems downstream. It’s critical to segregate all fuel and solvents as it is extremely difficult to remove and often requires complete renewal of all parts of a water system including the source.


Deciding on the most appropriate type of treatment for your supply is best left to an expert. At minimum, some form of disinfection, eg Ultraviolet (UV), will be needed to kill any bacteria in the water.

If there are particles in the water, at least one filtration stage will be needed to remove dissolved metals, and treatment may be needed too.

Following high rainfall, many supplies are coloured with organic matter washing into the water source. These compounds can reduce the effectiveness of ultra-violet disinfection systems and may need to be removed using special filters.

Most water sources in the area are naturally soft (this means they have a low concentration of natural dissolved minerals such as Calcium and Magnesium) and can be quite acidic (below 6.5 pH). Low pH waters can corrode metal pipework and presents a potential health risk from metals leaching into the supply. Filters containing alkaline media are commonly used to correct this.

Maintaining your treatment system

Any treatment installed will need to be maintained, so it will be an ongoing expense.

It’s important to regularly:

  • check the treatment system is performing correctly
  • carry out regular maintenance
  • record routine maintenance tasks and faults

If you can't do this yourself, it may be worth taking out a service contract with a reputable supplier who can keep your treatment system working to specification.

If you share your private supply with other properties, it is often more affordable to install a central treatment facility.

Cartridge filters

Cartridge filters are simple, modular filters, and can be used to remove particles, or sometimes chemicals, from your water. They work by trapping solid material in the water. Depending on their rating, they will remove particles above a particular size.

For many supplies, several filters in descending order of particle removal size will be needed eg 50 micron followed by 20 micron followed by 5 micron. The exact choice depends on the quality of the supply and the substance(s) that need to be removed. Filters down to 1 micron will sometimes be required.

As long as they're installed and used correctly, cartridge filters can remove sediment, metals and some microorganisms from the water. They’re a simple and robust technology that are often quite effective.

You should make sure that the filters are correctly sized for your water flow, otherwise they may get blocked.

Cartridge filters work best where there is not too much solid material in the water supply and little manganese or iron (less than about 300 microgrammes per litre of iron). You may need to use filters containing loose media if there's a significant quantity of sediment in the water, or high concentrations of iron and manganese.

Some filters have carbon in them to remove low concentrations of the organic compounds that cause colour in water.

A 5 micron filter is typically required before UV disinfection to ensure large particles don’t shadow pathogens as they pass through the treatment system. A smaller 1 micron filter may be required in certain circumstances where a source is particularly vulnerable.

Installing cartridge filters

Correct installation depends on your individual circumstances. So it may be best to consult a specialist contractor, otherwise you risk the filters not being effective, or blocking.

Choose filters that are approved by the Water Regulatory Advisory Scheme (WRAS) or NSF, the national public health and safety organisation.

Replacing cartridge filters

Cartridge filters need to be replaced once they become dirty or blocked.

How often they need to be changed depends on the quality of the water passing through them, and should be decided for each supply. It's best to keep stocks of spare cartridge filters in case you need them. Some coarse filters are reusable and gentle clean.

To change a filter:

  • turn the supply off
  • unscrew the housing
  • empty any water inside the housing
  • carefully replace the filter, taking care to achieve a good seal

If you’re changing your filter, make sure to use good hygiene practices to avoid contamination of the new filter. Contamination may introduce the risk of bacterial issues further down the supply.

Handle dirty filters with care and ensure they’re suitably disposed. There could be health risks associated with handling dirty filters, because bugs can be trapped in their debris.

Follow the manufacturer's instructions for your filter if you have them.

Media filters

Media filters are filters with loose granular media such as carbon, sand, grit or synthetic media inside. The media is typically contained within a plastic or fibreglass vessel about 1.5m tall.

If there’s not much solid material in your water supply, and little manganese or iron (less than about 300 micrograms per litre of iron), cartridge filters may be enough, and easier to use.

Media filters should be used where there is a significant quantity of sediment in the water or higher concentrations of iron and manganese.

Iron and manganese can cause problems in water supplies because they can:

  • have an impact on your water's colour, smell or taste
  • stain sanitary fittings and clothing
  • block ultra-violet disinfection systems and other vital treatment processes

How media filters work

Depending on the type of media used, solid and/or suspended particles in the water are trapped by the media. Clean water passed through and onto the next stages of treatment.

Over time, particles will build in the media and increase the head pressure which will make it harder to push water through resulting in a reduction in flow. A periodic backwashing cycle is required to clean the vessel and works by pushing water in the opposite direction to flush out impurities.

If the backwash cycle fails, there’s a risk of blockage or contamination breakthrough. Likewise, when used for a number of years, the media will become exhausted and will need to be replaced. This should be assessed regularly and carried out by a Specialist.

pH correction

Low pH water is often found in this area and has a health and maintenance risk associated to it. Low pH water can corrode pipework leading to excessive levels of lead, copper, nickel and zinc in the water supply.

Lead is harmful especially for young children’s development. When identified, replacement of all lead plumbing is essential.

Early warning signs of low pH water are leaks occurring or staining. Copper for instance is known to stain clothing or hair green.

High pH water is less common but can cause taste problems, corrode pipework and cause irritation to skin.

How pH correction works

Treatment to increase pH usually involves passing water through a neutralising filter containing alkaline media such as limestone or magnesium oxide. You should get advice from a specialist installer.

It's important that the filter's size, and the blend of media within it, is right for your water supply, otherwise the pH could be under, or over, corrected.

Installing a neutralising filter correctly depends on your individual circumstances, so it's best to consult a specialist installer.

Neutralising filters should generally be fitted after any other filtration, so that the media does not become clogged by debris.

Neutralising filters rely on alkaline media dissolving in the water to change the pH. The media is gradually used up in the process, and will eventually need to be replaced. It is important that the amount of media in the filter is regularly checked. This can be done by monitoring pH using a simple test, and seeing if there are any stains on fittings and sanitary ware.

If you do need to top up the media, make sure you use the right type. It is worth cleaning out the filter vessel from time to time and completely changing the media.

Alkaline media can be very corrosive, so it's best to follow your manufacturer's instructions, or get help from a professional.

UV disinfection

Ultraviolet (UV) is invisible high energy light radiation with a wavelength between 200-300 nanometres. Unlike mains water which used residual levels of chlorine, UV disinfection doesn’t affect the taste.

It can be used to kill or damage organisms that cause disease in drinking water, including some that cannot be killed by chlorine such as Cryptosporidium. UV lamps kill bacteria in your water, but won't change the taste.

UV systems require failsafe mechanisms such that when the power fails or if the UV lamp breaks, system users are notified to stop drinking the water. This is often done using a solenoid valve that closes upon a failure occurring.

It’s vital to have suitable pre-treatment to the UV as cloudy or water with large particles will prevent UV radiation passing through. Supplies with high levels of manganese and/or iron will need even more regular maintenance to ensure deposits don’t accumulate on the internal quartz sleeve and block UV radiation. Manganese and iron deposits present as a dark, reddish brown coloured layer.

Pre-treatment will usually consist of at least a 5 micron cartridge filter placed just before the UV lamp. More enhanced pre-treatment such as a 1 micron and/or media filters may be required depending on the source quality.

As with any water treatment system, you should get advice from a suitably qualified professional.

Keeping your UV system clean

Whilst UV disinfection is an effective and unintrusive disinfectant, it doesn’t leave any residual disinfectant in the water. For this reason it’s possible for water to be re-contaminated if pipes, tanks or taps downstream are not well maintained and secure. It is good practice to flush pipes and tanks with chemical disinfectant routinely to ensure water remains safe at the point of consumption.

UV systems themselves are relatively simple to maintain. The quartz sleeve inside the chamber will accumulate dirt over time and will require cleaning periodically to ensure its effectiveness– once per month typically. Even when cleaned regularly, UV bulbs will last for approximately one year before they begin to drop in efficiency and require replacement.

UV treatment systems come in a variety of sizes and it is important to ensure the correct specification is used for the peak flows your supply consumes. A rough calculation is 0.2m³ per person per day on a supply. Operating outside of the stated flow range may lead to insufficiently treated water passing downstream of the system.

Find suppliers of water treatment equipment and servicing

Changing a UV filter

Dirt can build up on the surface of the lamp and stop it from working effectively. This means disinfection will only be effective if you change the lamp regularly.

Most lamps need to be changed after a year. Some of them have a lamp-life countdown as a reminder. Check with your manufacturer to find out if yours has one.

You can change the UV lamp yourself, or you can organise for routine maintenance to be carried out by a contractor.

If you're going to do it yourself, you’ll need:

  • a spare lamp, spare sleeves and disposable gloves
  • to stop forward flow of water
  • turn off the power and let the UV filter cool down so you can touch the bulb safely
  • remove the safety cap at the top of the UV system by squeezing the tabs
  • remove the lamp sleeve (if there is one) along the sleeve bolt from the chamber
  • unscrew the UV lamp
  • install and secure the new lamp into sleeve
  • secure the lamp and sleeve assembly
  • insert the safety cap and plug the system in again

These are generic instructions. You should follow your manufacturer's instructions if you have them. If you’re unsure, seek advice from your maintenance contractor or Public Protection.

Switching UV systems on and off

If you only switch your filter on just before using your water it will not have enough time to get rid of the bacteria. Make sure you always keep your UV filter switched on, and have a plan for what you'll do if there's a power cut. It is good practice to leave your UV system on at all times so that downstream tanks or taps aren’t contaminated with harmful pathogens.

UV system isn't working

If there's a problem with your UV system, make sure no-one drinks the water unless it has been boiled or until you're sure it's being properly disinfected. You may need to take advice on an alternative way to disinfect your water supply until the UV is working. This should be detailed in your Drinking Water Safety Plan (DWSP).

As well as checking the quality of the incoming water and any pre-treatment, you should also replace faulty lamps and check if the:

  • UV lamps are operating
  • power supply's functioning
  • UV transmittance (the lamp's intensity) is reduced
  • quartz sleeves surrounding the lamps need cleaning or replacing
  • UV sensors are working

If your UV system seems to be working but you're still getting microbiological failures from samples, there could be a number of reasons such as the:

  • water supply is becoming re-contaminated after the UV system
  • UV system needs more maintenance and cleaning
  • incoming water isn't suitable quality for UV disinfection without pre-treatment
  • water isn't getting enough contact time with the UV
  • taps aren't clean and/or harbouring bacteria

UV system makes water warm

Your water may be warm when you first draw it because it's just left the UV chamber, or if there's a low flow of water through the unit and it's the wrong size.

If this happens, try flushing water through the system until cooler water appears.