Domestic water filters and softeners

What are they?

A range of water filters are advertised and sold for use within the home. These include jug filters which are stand alone and not connected to the water supply as well as filters and other devices plumbed in directly to the water supply. Manufacturers’ claims for these products sometimes cause consumers to become concerned about the quality of their tap water. It is not uncommon for marketing literature and promotional websites to suggest that purchase of a water treatment unit will remove contaminants from tap water. Common claims include:

• Removal of pesticides (activated carbon filters)
• Removal of minerals (reverse osmosis)
• Removal of taste or odour (activated carbon filters)
• Removal of particulate matter or colour (1 micron rated filters)
• Removal of hardness (water softeners and reverse osmosis)
• Removal of nitrates (ion exchange)

Are they necessary?

The quality of tap water in England and Wales is ranked amongst the highest in the world (https://epi.yale.edu/measure/2024/UWD). By law your local water company is required to supply wholesome water that is suitable for all domestic purposes, including drinking, cooking and washing. All public water supplies are regularly tested in England and Wales and the results which are published and available to every consumer on request show that tap water is safe to drink and there is no need to install additional treatment within the home as a health protection measure.

Pesticides

Although some raw water sources in England and Wales are at risk of contamination with traces of common pesticides, in these situations, water companies treat the water to remove pesticides to below the strict standards in the drinking water regulations. Home water treatment is not required.

Colour or particulate matter

Some water supplies may experience localised problems resulting in particulate matter or colour in tap water (see discolouration leaflet here). If the problem is due to a fault with pipes and fittings for which the building owner is responsible, then use of a suitable filter may improve the aesthetic water quality as a temporary measure. Before making a purchase, you should contact your water company for advice. It may be that maintenance on the water mains is planned to remedy a problem in the local supply network. If the fault relates to your own pipes and fittings, it is always best to employ a plumber to identify and remedy the root cause of the problem.

Taste or odour

The taste of tap water can vary between regions due to differing hardness (see Water Hardness leaflet) and residual concentrations of chlorine used to maintain the safety of drinking water in the network. Some consumers dislike the taste of tap water. This is especially so when living somewhere different from where you grew up as a child. Removing objectionable tastes and odours is the most common reason for purchasing a water filter. When choosing a filter for this purpose ensure it contains activated carbon and change the filter cartridge in line with the manufacturer’s instructions or it will cease to be effective and may leach other chemicals or bacteria. If you see small black particles in your water after treatment through an activated carbon filter these particles are unlikely to have originated from your tap water, instead they will be particles of activated carbon from the filter itself. Before decided to purchase a carbon filter, be aware that a more cost-effective solution is to store a clean, glass, covered jug of drinking water in the refrigerator.

Reverse osmosis systems

Reverse osmosis (RO) filtration systems remove most dissolved solids and soften the water producing a waste stream equivalent to 20-30% of the incoming flow. There is also a substantial reduction in pressure through the RO unit. Treatment by RO should be considered only for specialist domestic purposes like photographic processing or hydroponic culture. You should be aware that RO treatment changes the natural properties of tap water. Therefore, RO water is not generally considered suitable for drinking and cooking. When RO treated water is to be used for drinking purposes it is recommended by the World Health Organization that minerals should be added back. See www.who.int/publications/i/item/WHO-HSE-WSH-11.03 for more information. RO treatment is expensive and generally not a feasible option for domestic supply purposes for most homeowners.

Consumers should be aware that installation of RO treatment on a metered water supply will increase water bills by up to one third because of the waste stream. Also, by law consumers must give notice to their water company of their intention to install a RO system.

Water softeners

The most common home water treatment system is a water softener. Softeners involve an ion exchange process that replaces calcium and magnesium (hardness) with sodium. The benefits include reduced formation of scale in hot water systems and improved lather production and efficiency of appliances for clothes and dish washing. There are no health-based guidelines for water hardness but it should be noted that some water softeners can add significantly to the sodium content of drinking water (WHO, page 463). Artificially softened water should not be used to make up baby feeds (see How to make up baby formula – NHS). Water with a value of 100 mg/l (as CaCO₃ calcium carbonate) or less will be more corrosive to pipework which could lead to dissolution of plumbing metals such as lead, copper, brass and nickel.

If you are buying a water filter, softener or other products?

Before purchasing a water filter, softener or other product, contact your water company to obtain a free copy of the drinking water quality report setting out the results of tests on your home water supply. Water companies often publish a water quality summary on their website. This report will show the legal standards and the maximum and minimum levels present in your tap water. This should reassure you that treatment is not required to remove contaminants such as nitrates and pesticides to make your tap water safe to drink.

If you still wish to purchase a water treatment unit to improve the taste and hardness properties of your home water supply, then ensure that you buy only from a reputable supplier. Do not purchase any device from a door-to-door salesperson, particularly those offering to test your water to demonstrate it is contaminated. Scams of this type are not uncommon and should always be reported immediately to your local trading standards officer. Be wary of claims made when purchasing products online. Any product must adhere to regulation 4 of the Water Supply (Water Fittings) Regulations 1999. Please refer to the Water Regs UK website for further guidance: Water Regs UK Limited – Guidance. Any product must be compliant with these regulations and suppliers must be able to demonstrate such compliance, such as through UK certification. To install a device always use a qualified plumber and check in advance with your water company that the device meets the water fittings regulations. Always follow the manufacturer’s advice about cleaning and maintenance and the frequency of changing cartridges; failure to do so will cause a build-up of deposits, create a breeding ground for bacteria and leaching of removed material back into the drinking water. For some units like water softeners, it can be very important to backwash them regularly and replenish salt. If your property is unoccupied for a period, then the devices will need maintenance on your return. It is sensible to consider a taking out a regular service agreement when purchasing a water treatment unit.