Tap water
Private water supplies
Wells, springs and boreholes are not regulated or treated like mains water. If you are on one, the responsibility for its safety is yours.
The risks, by supply type
| Type | Principal risks | Note |
|---|---|---|
| Surface water — stream or lake | Microbiological contamination, turbidity, agricultural runoff | The highest-risk type. Needs filtration and disinfection |
| Spring | Microbiological contamination after rainfall; livestock access | Springs respond quickly to surface conditions, whatever their apparent purity |
| Shallow well or borehole | Microbiological contamination, nitrate, surface ingress | Vulnerable to anything on the land above |
| Deep borehole | Natural chemistry — iron, manganese, arsenic, fluoride, radon | Usually microbiologically safe; chemistry is the question |
| Rainwater harvesting | Microbiological contamination, roof material leaching | Not potable without treatment |
What to test for
- Microbiology — E. coli and enterococci, at minimum. This is the non-negotiable test
- Nitrate, if there is arable land in the catchment
- Iron, manganese, pH and hardness, which affect usability rather than safety
- Arsenic, fluoride and radon, depending on local geology — your local authority will know what is relevant
- Lead, if the property has lead pipework
- Pesticides, if there is intensive agriculture nearby
Test at least annually, and always after heavy rainfall or flooding, after any work on the supply, and when buying a property served by one. In the UK, local authorities have a statutory duty to risk-assess and sample private supplies, and are the first place to ask.
Treatment for a private supply
- Protect the sourceFence livestock out, cap and seal the wellhead, divert surface runoff away. The cheapest and most effective barrier by far.
- Pre-filter for sedimentRemoves particles that would otherwise shield organisms from disinfection and foul later stages.UV cannot work through turbid water — this stage is not optional if UV follows.
- Treat specific chemistryIron and manganese removal, pH correction, or specific media for arsenic or fluoride where the local geology requires it.
- DisinfectUV is the usual choice for a private supply: effective against bacteria, viruses and Cryptosporidium, and no chemical handling.
- Monitor and maintainReplace UV lamps annually whether or not they still light — output falls long before failure. Service filters on schedule. Re-test after any change.
Sources
- Drinking Water Inspectorate — Drinking water quality in England and Wales. Open — attribution required · Open Government Licence v3.0
- World Health Organization — Guidelines for Drinking-water Quality. Public but restricted · CC BY-NC-SA 3.0 IGO
- UK Health Security Agency — Waterborne infectious disease surveillance and guidance. Open — attribution required · Open Government Licence v3.0