The Three Water Test Demonstrations That Measure Nothing

In-home water treatment sales has a long tradition of demonstrations that look like science and are not. They are effective precisely because they are visual, dramatic, and happen too quickly to question.

Here are the three you are most likely to see, and what each is really showing.

1. The electrolysis demonstration

What you see: A device with two metal electrodes is placed in a glass of your tap water and switched on. Within a minute the water turns brown, orange or black, often with a scum forming on top. A second glass of bottled or treated water stays clear. The conclusion offered is that your water is full of contaminants.

What is happening: The electrodes are typically iron and aluminium. Passing current through water corrodes the iron electrode, and the resulting iron hydroxides colour the water brown. The colour comes from the device, not from your water.

Why the other glass stays clear: Electrolysis requires dissolved ions to carry current. Purified or distilled water has very few, so very little current flows and the electrode barely corrodes. It is not that the purified water is clean — it is that it is a poor conductor.

You can produce the same brown water using bottled mineral water. The demonstration measures conductivity, badly, and presents the result as contamination.

2. The TDS meter as a safety test

What you see: A handheld meter is dipped into your water and shows a number in parts per million. A higher number is presented as worse. Sometimes it is compared against bottled water or reverse osmosis water to make the gap dramatic.

What is happening: A TDS meter measures electrical conductivity and converts it into an estimate of total dissolved solids. That is a real measurement of a real thing. It just does not mean what it is being used to imply.

TDS cannot distinguish calcium from arsenic. It does not detect bacteria, because bacteria are not dissolved solids. It does not meaningfully detect PFAS, most pesticides, or most organic chemicals, because those are poor conductors. Water with a TDS of 300 can be excellent; water with a TDS of 30 can be dangerous.

There is a second layer to this one worth knowing: a water softener does not lower TDS. Ion exchange swaps calcium and magnesium for sodium, so the hardness goes and the dissolved solids stay. A meter reading taken after a softener proves nothing about whether the softener works.

3. The precipitation or “soap” demonstration

What you see: A reagent is added to your water and it turns cloudy, milky or forms a curd. The same reagent in treated water stays clear.

What is happening: This one is closer to legitimate, and that is what makes it slippery. Reagents that precipitate with hardness minerals genuinely indicate hardness. Soap that fails to lather genuinely indicates hardness.

The problem is what gets claimed from it. Hardness is a real and measurable condition, and titration will give you a number in grains per gallon. A cloudy glass gives you a feeling. When a cloudy glass is used to imply contamination rather than hardness, or to justify a system without ever producing the number, the demonstration has stopped being a test.

What a real water test looks like

You should see numbers, and you should leave holding them. Hardness in grains per gallon. Iron and manganese in milligrams per litre. pH. A named laboratory for anything microbiological or health-related, because bacteria, lead, nitrate, arsenic and PFAS cannot be measured with a field kit no matter what anyone says.

You should also be told which results are unremarkable. A test where every single number is presented as a problem is a sales document, not a measurement.

The other warning signs

• A price that is only available today.
• A recommendation made before the measurement.
• No written results left with you.
• Claims that a system removes a contaminant, without a certification listing naming that contaminant for that specific model.
• Health or medical claims of any kind.
• Reluctance to tell you who performs the plumbing work and under whose licence.

None of this means every in-home water test is a con. It means the demonstrations above are not evidence, and a company that needs them is telling you something about itself.