How we check
How Tap Sorted treats claims, costs and sources
Filter pages mix manufacturer statements, standards numbers and customer opinion, and it is hard to see which is which. This page explains the labels we use, what we rely on, and how far the evidence on this site currently goes.
Three kinds of evidence, kept apart
- Manufacturer claim. What a maker states, with where and when it was read. A claim is a starting point, not proof.
- Independent confirmation. The exact model appears in an independent certification listing for the standard and claim in question. A maker’s own page can’t earn this label. The certifications guide shows how to check one yourself.
- Hands-on observation. Something we have seen in use. We haven’t tested any products, so there are none to report.
Product comparisons and calculator examples
The guides explain filter types and buying checks. We have not tested or ranked individual products.
The running-cost calculator uses clearly labelled illustrative examples. Enter the figures for a model you are considering to compare its purchase and cartridge costs.
How the cost figures work
The running-cost calculator counts from the day a filter is fitted and totals the cost at one, three and five years. Cartridges in the purchase price aren’t charged again, each cartridge follows its own schedule, and a set due exactly at the end of a period falls into the next one. A change is due at the time limit or the volume limit, whichever arrives first, with a month taken as 30.44 days. Anything missing gives an “incomplete” total rather than £0. The replacement guide walks through it with examples.
Sources we rely on
- Drinking Water Inspectorate: domestic water filters and softeners. Official guidance for England and Wales: how filter types differ, checking your supplier’s information, scrutinising claims, keeping up replacement, and its cautions on reverse osmosis.
- NSF: standards for water treatment systems. What NSF/ANSI 42, 53 and 58 each address. Standard numbers are categories, not rankings.
- WRAS approvals directory. A voluntary approval of fittings and materials, with conditions of use. It doesn’t guarantee a compliant installation and says nothing about what a filter removes.
- Water Supply (Water Fittings) Regulations 1999 and WaterRegsUK’s England requirements. The rules for fittings connected to the public supply in England and Wales, including which installations must be notified. Scotland and Northern Ireland have their own.
- Drinking Water Inspectorate: water hardness. What hardness is, used in the limescale guide.
The guides give general information. Where fitting is involved, the manufacturer’s instructions for the exact model and a qualified plumber come first. We don’t give health advice, and the site can’t tell you what is in your own water; your supplier publishes that information for your area.