Water quality & standards
Water testing: what home kits can and cannot tell you
Home test strips and TDS meters answer a narrow set of questions. Understanding which questions they answer — and which they only appear to — is most of the value.
Home water testing has become cheap and widely marketed. Some of it is genuinely useful. Some of it measures something other than what the packaging implies.
What each method actually measures
| Method | What it measures | Genuinely useful for | Cannot tell you |
|---|---|---|---|
| TDS meter | Electrical conductivity, converted by an assumed factor | Checking an RO membrane is still working; comparing two waters | Anything about safety, or what the dissolved solids are |
| Test strips | Colour change against a few parameters | Rough hardness, pH, chlorine, sometimes nitrate | Precise values; metals; organics; pathogens |
| Hardness titration kit | Calcium and magnesium by drop count | Reasonably accurate hardness, useful for softener sizing | Anything else |
| Bacterial presence test | Growth of indicator organisms | Presence or absence of coliforms, useful for private supplies | Which organism, how many, or whether it is pathogenic |
| Accredited laboratory analysis | Specific analytes to a stated detection limit | Definitive results for metals, nitrate, pesticides, PFAS, microbiology | Anything outside the analyte list you paid for |
When laboratory testing is worth it
- You are on a private supply — a well, spring or borehole — with no treatment or monitoring. This is the case where testing is genuinely important.
- You have or suspect lead pipework, and want a lead result from your own tap.
- You live near a known contamination source such as a firefighting training site, landfill or industrial facility.
- A specific problem has appeared: persistent taste, odour, discolouration or illness.
- You are buying a property with a private supply.
Getting a meaningful result
- Use an accredited laboratoryLook for ISO 17025 accreditation for the specific analytes you want. Accreditation is analyte-specific, not laboratory-wide.
- Ask for the right analyte listA "full analysis" is never full. Decide what you are looking for — metals, nitrate, pesticides, PFAS, microbiology — and confirm it is included.
- Follow the sampling protocol exactlyFor lead, whether you flush the tap first changes the answer several-fold. For microbiology, sterile technique and prompt delivery are essential.Most poor results are sampling errors rather than water problems.
- Check the detection limitA "not detected" result means "below the reporting limit", which may be far above a level of concern for something like PFAS.
- Interpret against the right standardUse the standard for your jurisdiction, and check whether the value is a legal limit, a guideline or an aesthetic objective.
Sources
- International Organization for Standardization — ISO water quality and water footprint standards. Permission required · ISO copyright — standards sold per document
- Drinking Water Inspectorate — Drinking water quality in England and Wales. Open — attribution required · Open Government Licence v3.0
- NSF International / American National Standards Institute — NSF/ANSI drinking water treatment unit standards. Public but restricted · Publisher terms — public access, reuse not clearly granted