What this guide can do
This guide helps organise the first questions. It cannot diagnose contamination, interpret an unexplained illness or design treatment for a private supply.
1. Check the immediate position
If a supplier, local authority or public-health body has issued a boil-water, do-not-use or other instruction, follow it. Do not substitute a domestic filter or this guide.
For a mains-water problem, start with the water company and DWI consumer reporting route.[1] For a private supply, use the local-authority route. DWI says local authorities implement the private-water-supply regulations through risk assessment and monitoring.[4]
2. Identify the supply
Record one of these before doing anything else:
- mains water supplied by a water company;
- a well, borehole, spring or other private source;
- a shared private distribution arrangement;
- an issue that may arise between the property boundary and a particular tap.
The answer controls which report, regulator and sampling route is relevant. It also prevents supplier-area data from being presented as a measurement at one kitchen tap.
3. Inventory the evidence
Create a short evidence table:
| Evidence | What to record |
|---|---|
| Supplier report | company, supply zone, reporting period, parameter and range |
| Household laboratory report | laboratory, accreditation scope, sample point, date, method, unit and reporting limit |
| Home screen or meter | exact device, method, range, unit, date and limitation |
| No current evidence | the question that needs an official or laboratory route |
UKAS provides a directory that can be searched by organisation type, name, region or category.[9] Directory presence is not enough on its own; the relevant method or activity must sit within the organisation’s current accreditation scope.
4. Name the problem carefully
Keep these categories apart:
- an official or health-related concern;
- taste, odour, colour or particles;
- measured hardness and scale;
- pressure, flow, storage or building plumbing;
- leak detection or shut-off planning.
A symptom is a reason to investigate. It is not a contaminant identification.
5. Decide where the outcome is needed
Point-of-entry treatment acts near the incoming supply. Point-of-use treatment acts at a particular outlet. Some systems use several stages. DWI describes a multi-barrier approach in which individual processes prepare water for downstream stages.[5]
That principle does not provide a household prescription. Source water, measured parameters, flow and maintenance capacity still control the design.
6. Write the pre-purchase brief
Before collecting quotations, record:
- supply type and responsible authority;
- evidence and sample context;
- exact outcome required;
- treatment location;
- peak flow and pressure information;
- space, drainage, electrical and bypass constraints;
- exact evidence expected from the supplier;
- consumables, service and verification plan;
- what happens during failure, alarm or power loss.
7. Know when to stop
Stop the product search and use an official, laboratory, medical or qualified professional route when:
- an active official notice applies;
- illness or exposure is suspected;
- microbiological contamination or a serious contaminant is suspected or reported;
- units, sample point or method are unclear;
- a private supply lacks a suitable risk assessment or analysis;
- treatment requires consequential plumbing, electrical or system design.
Next steps
- Evidence unclear →
/water-testing/ - Point-of-entry question →
/whole-house-treatment/ - Drinking/cooking outlet →
/drinking-water-systems/ - Measured hardness →
/hard-water-softening/ - Microbiological/UV context →
/uv-water-treatment/ - Upkeep and five-year cost →
/costs-maintenance/