Treating a private water supply

You'll always need to disinfect your water for it to be safe.

Ultraviolet (UV) disinfection is the most common option. Other options, like chlorine or chlorine dioxide, need a specialist to install them.

UV disinfection

A UV disinfection system uses UV lamps to kill bacteria in your water. It will not change your water's taste.

The UV radiation needs to be able to pass through the water. It will not work on very cloudy or coloured water, for example from peaty soils.

Other substances in the water, like iron and manganese, can reduce the UV's effectiveness. UV needs a power supply to work.

If you find UV disinfection alone is not enough, you can add pre-treatments, such as cartridge filters, to your supply as well.

When using UV disinfection:

• keep your pipes and tanks in good condition
• regularly clean the quartz sleeve on the UV lamp
• UV lamps get less effective over time and typically need replaced annually
• set up an alarm to alert you if the UV lamps stop working

If you're considering this treatment or need help to maintain it, get advice from a specialist.

If you find UV disinfection is not enough on its own you may need to add other treatments like filters.

There are 2 main types of filters you can use to remove dirt, sediment and some bacteria from your water supply:

• cartridge filters
• media filters

Cartridge filters

Cartridge filters are easy to fit. They remove particles, sediment, metals and some bacteria from your water.

You may need to use several filters of different sizes in order to trap different sizes of materials. Filter sizes are measured in microns. The size will be marked on the filter or box, for example 10 microns.

Place your filters in size order. The largest micron size should be furthest from your tap, the smallest micron size should be nearest your tap.

Choose filters that are approved by the Water Regulatory Advisory Scheme. ​​​​

You'll need to replace filters that are dirty or blocked. You cannot reuse them. Keep stocks of replacements. Follow the manufacturer's instructions for replacing them.

Media filters

Media filters have loose grains like sand or grit inside. The grains sit in a plastic or fibreglass shell.

Use these type of filters if your water has:

• a lot of sediment
• high concentrations of iron and manganese, which can affect ultraviolet disinfection

The filters trap the solid material that's in the water, letting clean water pass through.

You need to clean these filters regularly using a process called backwashing. This is where you pass water (and sometimes air) back through the filter. This removes dirt and cleans the filter. 

Most media filters have a timing mechanism to trigger regular backwashing.

pH measures the acidity of water. Water with the wrong pH can taste bad, corrode metal pipes and irritate skin.

pH correction passes water through a neutralising filter that has limestone chips or magnesium oxide to correct the pH.

The limestone or magensium oxide is gradually used up in the process, and will eventually need replaced.

If you're considering pH correction treatment, get advice from a specialist.  You should position it in between any filters and your disinfection treatment.

To maintain pH correction you'll need to:

• regularly monitor the pH of the water, as this will indicate if the neutralising filter has enough limestone or magnesium oxide
• top up the limestone or magnesium oxide when required
• occasionally clean out the filter casing and change the limestone or magnesium oxide

limestone or magnesium oxide can be very corrosive. Follow the manufacturer's instructions or get help from a specialist when replacing these.