Hard water signs: how to tell, and how to confirm it.

What hard water is

Hard water is water carrying a lot of dissolved calcium and magnesium. Both come from rock. Rain that soaks through limestone, or sits in a granite aquifer for years, picks them up on the way. Borewell water is usually harder than piped surface water for that reason, and it gets harder through a dry summer as the water table falls.

The Indian drinking water standard, IS 10500:2012, sets two limits for total hardness, measured as calcium carbonate: 200 mg/L is the acceptable limit, and 600 mg/L is permitted only where no better source exists. Water inside the first limit still leaves some scale. Water near the second leaves a lot. Hardness is limited because of what the minerals do to pipes, heaters, soap and skin, not because calcium and magnesium are harmful at those levels.

Hardness is not the same thing as TDS, though the two often rise together. A TDS meter counts everything dissolved and cannot tell calcium from sodium. The TDS vs hardness guide explains the difference. It matters here because the most common way people "check" for hard water, a TDS pen, does not check for it at all.

The seven signs

None of these proves hardness on its own. Three or four together make it very likely.

1. White crust on taps and shower heads. Chalky, builds up where water dries, does not wipe off with a cloth. Shower heads start spraying sideways as the holes block.
2. Soap that will not lather. The first squeeze of soap goes to reacting with the minerals, not to cleaning. You use more, and a grey scum forms on the water and on the bucket.
3. Stiff, dull laundry. Towels dry rough. Whites go grey. The scum that formed in the wash settles into the cloth and stays there.
4. White spots on utensils and glass. Steel and glass dry with a chalky film that comes back after every wash. Dishwashers show it worst.
5. Scale in the kettle and the geyser. A hard white layer in the kettle within weeks. A geyser that takes longer to heat than it used to, and then fails at the element.
6. A film on tea. A thin sheen on the surface of a cup of tea is the calcium reacting with the tannins.
7. An RO membrane that dies early. If the purifier's membrane needs replacing well inside its expected life, and the sediment filters were changed on time, scale on the membrane is the usual reason.

Two things get mistaken for hardness. White spots that dissolve in plain water are salt left behind by evaporation, which is TDS, not hardness. A slippery feel in the shower is the opposite condition; soft water feels that way because the soap is rinsing off properly instead of stopping in a scum.

A rough test at the kitchen counter

There is a quick check that costs nothing. Half fill a clear bottle with the tap water. Add a few drops of plain liquid soap, not detergent. Cap it and shake hard for ten seconds. Soft water makes a tall head of foam and stays clear underneath. Hard water makes little foam, and the water goes cloudy with scum. It is a rough test. It tells you which side of the line you are on, not how far. Do not size a softener from it.

Vinegar gives a second rough check. Put a drop on the white crust from a tap. If it fizzes, the crust is carbonate scale, which is hardness. If nothing happens, it is something else.

How to confirm it properly

Three ways, in rising order of cost and accuracy.

Test strips. A strip dipped in the water changes colour against a chart. Cheap, fast, and coarse. The bands are wide, so a strip will tell you "hard" but not whether that means a little over the limit or three times it. Fine for a first answer.

A drop-count kit. The kit that softener installers carry. A measured sample, a drop of indicator that turns it red, then a reagent added one drop at a time until it turns blue. The number of drops gives the hardness. Accurate enough to size a softener and to check that one is working. It costs a few hundred rupees and does dozens of tests.

A lab report. A certified lab reports total hardness as CaCO₃ along with calcium and magnesium separately, and everything else in the water. It is the only test that also finds the things hardness has nothing to do with. If the source is a borewell, get this done once; the borewell water guide explains which two tests to ask for.

Whatever the method, write the figure down with the date. Hardness on a borewell moves with the season, and you will want the before figure when you check whether a softener is doing its job.

What the number tells you to do

Under 200 mg/L, inside the acceptable limit, hardness is rarely worth spending on. Soak the shower head in vinegar now and then and move on. Between 200 and 600, the nuisance is real and the decision is about where it hurts. If the problem is hair, skin and laundry, the hair and skin guide goes through what helps. If the problem is the geyser and the washing machine, the appliance damage guide works out what ignoring it costs. Above 600, beyond even the permitted limit, a softener stops being a comfort purchase, and the cost guide gives the price ranges.

One thing a hardness result does not settle is drinking water. A softener does not make water safe to drink, and an RO purifier does not stop scale in the bathroom. They are different jobs, and the softener vs RO guide takes each in turn. LUXGEN makes RO purifiers and their spares. It does not make a softener; those are on DraQua.