Under-sink water filters for UK homes

“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.”

“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.”

“There is also a substantial reduction in pressure through the RO unit.”

“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.”

Source: Drinking Water Inspectorate, Domestic water filters and softeners ↗

Each pick's card states the maker's pressure range and the connection it ships with, from the maker's manual and product page linked in Sources. US fittings are not UK sizes, so have a plumber confirm the connection and your water pressure before you buy, and tell your water company before you fit reverse osmosis.

“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.”

Source: Drinking Water Inspectorate, Domestic water filters and softeners ↗

Our under-sink pick is not listed for lead, so it is not a lead filter. If you have lead pipes, the inspectorate's advice is to replace them: “This short-term measure will protect you and your family, but if there are lead pipes or another source of lead present, these should be replaced as soon as possible.”

Source: Drinking Water Inspectorate, Lead in Drinking Water ↗

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Is WRAS approval the same as a filter certification?

No. WRAS approves water fittings and materials to the Water Supply (Water Fittings) Regulations 1999; its tests cover what the fitting does to the water, such as odour, flavour and leaching of metals. What a filter removes is shown by an NSF, WQA or IAPMO listing for the exact model.

Do I have to tell my water company before fitting reverse osmosis?

Yes. The Drinking Water Inspectorate says that by law you must give notice to your water company of your intention to install a reverse osmosis system.