Conductivity
How well the water carries a current, which is a fast proxy for how much is dissolved in it.
- Measured in
- uS/cm
No range is shown because none is published. Conductivity is a proxy rather than a contaminant, and total dissolved solids is the row that carries the published figure — banding both would judge the same water twice against one standard.
What it is
Pure water barely conducts electricity. Dissolved ions — salts, minerals, metals — let it carry a current, and conductivity measures how well. It is the raw measurement that a TDS meter converts and displays as a solids figure.
Why it matters
Conductivity is the cheapest, fastest thing you can measure about water, and its value is as a tripwire rather than as a verdict. It tells you the total dissolved load has changed; it cannot tell you what changed or whether the change matters. A stable reading that suddenly moves is a genuinely useful signal on a private well — intrusion, a failing softener, a new source — and is worth a laboratory panel. A steady reading tells you nothing is changing, which is most of what routine monitoring is for.
How to measure it
A cheap handheld meter, and this is one of the few readings where the inexpensive instrument is genuinely the right tool.
Digital meter or pen
- How trustworthy
- Dependable
- Cost
- Mid range
- Effort
- Seconds to read, minutes to calibrate
A probe on a handheld body that reads the water electrically and prints a number. No colour to judge, which removes the commonest source of error and introduces a new one: a meter that has drifted looks exactly as confident as one that has not.
A conductivity or TDS pen reads in seconds. Buy one that shows conductivity directly rather than only a converted solids figure — the conversion uses an assumed factor that is wrong for your water in an unknown direction.
Watch out: Conductivity rises with temperature, substantially. A meter without automatic temperature compensation will read a cold winter sample and a warm summer one as different water when nothing has changed.
Where to find it: Online and in pool and aquarium shops. Buy the calibration solution at the same time; a meter without it is a guess with a decimal point.
Certified laboratory, mail-in kit
- How trustworthy
- Reference grade
- Cost
- Most expensive
- Effort
- Careful sampling, then days or weeks of waiting
You are posted bottles and instructions, you fill them exactly as told, and you post them back. Weeks later a report arrives with figures nobody has to interpret by eye. This is what a result you intend to act on should be built from.
Included on any general chemistry panel, measured at a controlled temperature, and worth having once as the baseline your pen readings are compared against.
Where to find it: State-certified drinking water laboratories; your state's certification officer keeps the list, and many public health departments will point you at one.
Taking the sample
For several of these the sample is where the error is, and no instrument recovers from a bad one.
- • Take the reading at a consistent temperature and from the same tap each time. This measurement is only useful as a trend, and a trend built from inconsistent samples is noise.
Further reading: US EPA: Consumer Confidence Reports, the annual report every community water system publishes
If it is too low
Very little dissolved. Typical of reverse osmosis or distilled water, and of some surface supplies. Very low conductivity water is aggressive toward metal plumbing.
- • Check pH and alkalinity if the water is also soft. Low-mineral water is corrosive and that is what dissolves copper and lead out of pipes.
If it is too high
A high dissolved load. Not a health finding on its own — it says nothing about which ions — but a reason to run a panel, especially if it has risen.
- • Run a general chemistry panel to find out what is actually dissolved. The number itself does not identify anything.
- • Compare against your own history rather than against a general expectation; what matters is the change.
Common questions
What is the difference between conductivity and TDS?
Conductivity is what the meter actually measures. TDS is that number multiplied by an assumed conversion factor, which depends on which ions are present — so two waters with identical conductivity can hold genuinely different amounts of dissolved solids. Conductivity is the honest reading; TDS is an estimate derived from it.
Does low conductivity mean the water is safe?
No, and this is the misreading that sells filters. Conductivity responds to dissolved ions in bulk, and the contaminants people most worry about are dangerous at concentrations far too small to move it. Water with almost no conductivity can still hold a harmful amount of arsenic, lead or bacteria.
WiseWaterGauge helps you record and understand your own readings. It is not a substitute for a certified laboratory test, and nothing here is medical or regulatory advice. If a health parameter is out of range, confirm it with an accredited lab and speak to your water provider.