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Water 🇬🇧 UK regulations; treatment limits from US and German technical guidance

Water filters for a private well or borehole in the UK: which you need and in what order

Choose treatment from a water analysis, not a brochure. For a private supply the Drinking Water Inspectorate advises treating the whole supply rather than one tap [1]. A typical line is sediment filter, iron and manganese removal, softener and UV at 40 mJ/cm² or more [2], with reverse osmosis at the kitchen tap only when the salts themselves are the problem. Equipment must comply with the Water Fittings Regulations, shown by UK certification such as WRAS [3].

Updated 2026-09-29 · every regulation and price links to its source at the bottom of the page. A guide, not a construction design.

Whole-house treatment or a filter under the sink?

“The Inspectorate advises whole supply treatment in preference to POU wherever possible” [1]: a point-of-use filter leaves every other tap untreated, so it is acceptable only after a risk assessment. Disinfection and iron removal belong where the water enters the house; an under-sink unit is an extra for drinking water.

Do you need a sediment filter?

We found no UK rule requiring one, but UV needs clear water, with turbidity below 1 NTU after a pre-filter [2]. For comparison, Germany makes an 80–150 µm mechanical filter at the house inlet compulsory, cleaned or replaced at least every six months [4], and one US county requires a 5 µm filter directly before a UV lamp [5].

How do you remove iron and manganese?

UK limits are 200 µg/l of iron and 50 µg/l of manganese [6]. The method depends on concentration and pH; the ranges below come from US university extension guidance:

What does a water softener do?

It swaps calcium and magnesium for sodium, so scale stops forming, but it does not lower total dissolved solids [12] and does nothing against microbes [13]. The UK has no hardness standard, and the DWI advises keeping an unsoftened kitchen tap for drinking and cooking [3].

Choose water treatment from your test →

What is a carbon filter for?

Activated carbon removes chlorine, tastes and odours, pesticides and other organics, and radon. It does not remove salts or hardness, and a cartridge left in too long lets contaminants break through [14]. It handles hydrogen sulphide (the rotten-egg smell) up to about 1 mg/l; higher levels need an oxidising filter or chlorination [15].

Reverse osmosis: under the sink or whole house?

RO removes most dissolved salts, including sodium, chloride and nitrate [14]. The DWI notes that it sends 20–30% of the incoming water to drain, that RO water is generally not considered suitable for drinking without remineralisation, and that on a mains supply you must notify your water company before installing one [16]. Most household systems sit under the sink; whole-house RO costs far more to buy and run [17]. An under-sink unit can be found for about £287 on offer (usually £378), and the same seller says typical systems cost £400 or more (approximate, as of September 2026) [18].

When do you need a UV steriliser?

When bacteria are found, or as a safeguard on a well or borehole. DWI guidance: a dose of about 40 mJ/cm² or more, clear water, iron and manganese reduced to around 200 and 50 µg/l first, the lamp replaced every 10–12 months, and a UV intensity sensor with an alarm, because water passes untreated if the lamp fails [2]. UV does not remove chemicals [13]. WRAS-approved units cost about £437–1,103 depending on flow (approximate, as of September 2026) [19].

In what order should the equipment go?

StepEquipmentWhy here
1Sediment filterProtects everything after it; UV needs clear water [2]
2Iron and manganese removalOxidised iron fouls softener resin, so it comes first [11] [20]
3SoftenerHardness scales the UV sleeve and the RO membrane [5] [17]
4Carbon, if neededTaste, smell, leftover chlorine after oxidation [10]
5UVLast on the whole-house line, on clear treated water [2]
6RO at the kitchen tap, optionalOnly when salts, nitrate or sodium are the problem [16]

Choose water treatment from your test →

What approvals should the equipment have?

Any device must comply with regulation 4 of the Water Supply (Water Fittings) Regulations 1999, backed by UK certification such as WRAS [3]. Be sceptical of magnetic or electronic ‘softeners’: a Bavarian environment agency review found they do not change hardness and their effect is unproven [21]. In Scotland a council grant of up to £800 per property can help pay for treatment [22].

Ask the assistant →

Frequently asked questions

Do I need a UV filter on a private borehole?

If the analysis finds bacteria, yes; the DWI sets out the dose, pre-treatment and alarm it expects [2].

Can a water softener remove iron?

Only dissolved iron below about 5 mg/l, and oxidised iron clogs the resin [11].

Is reverse osmosis water safe to drink?

The DWI says RO water is generally not considered suitable for drinking without remineralisation [16].

Do magnetic water softeners work?

Hardness stays the same and their effect is unproven [21].

Is there a grant for private water supply treatment?

In Scotland, up to £800 per property; we found no equivalent in England or Wales [22].

Read also:Private water supply testing UK: what to test and costWater softener for very hard or mineral-rich water: UK guideWater softener installation UK: drain, bypass and brine

Sources

  1. Drinking Water Inspectorate — Private water supplies treatment guide: Point of use treatment, Point of use treatment (UK) · recommendation · checked 2026-09-29 · source
  2. Drinking Water Inspectorate — Private water supplies: treatment guide, UV disinfection, UV disinfection (UK) · recommendation · checked 2026-09-29 · source
  3. Drinking Water Inspectorate — Domestic water filters and softeners, Water softeners (UK) · recommendation · checked 2026-09-29 · source
  4. dvgw.de, Mechanisch wirkende Filter (DE) · regulation · checked 2026-09-29 · source
  5. Chautauqua County (NY) Environmental Health Services — Private Drinking Water Standard for Ultra Violet (UV) Light Disinfection System, Water Quality; installer checklist (US) · regulation · checked 2026-09-29 · source
  6. The Private Water Supplies (England) Regulations 2016 (SI 2016/618), Schedule 1, Part 1, Table B, Part II (national requirements) (UK) · regulation · checked 2026-09-29 · source
  7. Penn State Extension — Iron and Manganese in Private Water Systems, Other Options (aeration, catalytic carbon, polyphosphate) (US) · recommendation · checked 2026-09-29 · source
  8. Penn State Extension — Iron and Manganese in Private Water Systems, Oxidizing Filters (Birm) (US) · recommendation · checked 2026-09-29 · source
  9. Penn State Extension — Iron and Manganese in Private Water Systems, Oxidizing Filters (US) · recommendation · checked 2026-09-29 · source
  10. Penn State Extension — Iron and Manganese in Private Water Systems, Oxidation followed by filtration (US) · recommendation · checked 2026-09-29 · source
  11. Penn State Extension — Iron and Manganese in Private Water Systems, Water Softeners (US) · recommendation · checked 2026-09-29 · source
  12. Montana State University Extension Water Quality — Hardness fact sheet, Treating Hard Water (US) · recommendation · checked 2026-09-29 · source
  13. CDC — A Guide to Drinking Water Treatment Technologies for Household Use (2012), Reverse Osmosis; Ultraviolet; Water Softeners; Filtration (US) · recommendation · checked 2026-09-29 · source
  14. University of Nebraska–Lincoln Extension EC703 «Drinking Water Treatment: An Overview» (rev. 2014), Table I (problem → treatment); Table II (methods) (US) · recommendation · checked 2026-09-29 · source
  15. Penn State Extension — Hydrogen Sulfide (Rotten Egg Odor) in Water Wells, Treatment options (US) · recommendation · checked 2026-09-29 · source
  16. Drinking Water Inspectorate — Domestic water filters and softeners, Reverse osmosis systems (UK) · recommendation · checked 2026-09-29 · source
  17. University of Nebraska–Lincoln Extension G1490 «Drinking Water Treatment: Reverse Osmosis» (rev. 2014), Treatment principles; Equipment (US) · recommendation · checked 2026-09-29 · source
  18. UK Water Filters — Under-sink reverse osmosis water filter system (UK) · price · checked 2026-09-29 · ~ · source
  19. Aquacure — Stainless steel UV steriliser systems (WRAS approved AC UV) (UK) · price · checked 2026-09-29 · ~ · source
  20. Pentair Fleck 5600SXT Upflow Service Manual, Installation: Water Pressure, Electrical Facilities, Existing Plumbing, Location Of Softener And Drain, Bypass Valves (US) · recommendation · checked 2026-09-29 · source
  21. Bayerisches Landesamt für Umwelt, Merkblatt Nr. 1.6/5 «Alternative Wasserbehandlungsgeräte zur Verminderung der Steinbildung in Hausinstallationen» (Stand Juli 2010), 1 Hintergrund; 4 Schlussfolgerungen (DE) · recommendation · checked 2026-09-29 · source
  22. mygov.scot — Apply for a private water supply grant; The Private Water Supplies (Grants) (Scotland) Regulations 2006, Grant (UK) · regulation · checked 2026-09-29 · ? · source

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