💧 Water guide

How to Check Your Water's TDS — and What the Reading Means

6 min readPublished 2 April 2026Updated 1 August 2026

What you need and what it costs

Tool	Cost	What it tells you
Digital TDS meter	₹250-500	Total dissolved solids in ppm. The basic technology decision
pH meter or strips	₹150-600	Acidity/alkalinity. Useful after RO, mostly for taste
Hardness test strips	₹200-400	Calcium and magnesium — decides whether you need softening
Home chemical test kit	₹500-1,500	Indicative chlorine, nitrate, iron. Screening, not diagnosis
NABL lab test	₹800-2,500	The real answer: metals, arsenic, fluoride, nitrate, bacteria

Tip

The ₹300 meter is enough to make the RO-or-not decision. The lab test is what you order if you are on groundwater, if anyone in the household is pregnant or an infant, or if your district has a known contamination issue.

Measuring properly, in six steps

Step 1 — Run the tap for 30 seconds first. Water that has been standing in the pipe overnight is not representative of your supply.
Step 2 — Collect in a clean glass, not a plastic bottle that previously held anything else. Rinse the glass with the same water twice before filling.
Step 3 — Let it reach room temperature. TDS meters compensate for temperature, but they compensate best near 25 °C.
Step 4 — Remove the meter's cap, switch it on, and immerse the probe to the marked line. Do not submerge the body.
Step 5 — Stir gently and wait for the reading to stabilise, which takes 10-20 seconds. Take the stable number, not the first one shown.
Step 6 — Rinse the probe in clean water and dry it before storing. A probe left dirty drifts, and a drifted meter is worse than no meter.

When to measure, and why once is not enough

Indian supply is seasonal in ways that matter. Municipal water blended with borewell in summer can run several hundred ppm higher than the same tap in monsoon. Tanker-fed supply varies with whichever source the tanker drew from that week. Coastal groundwater rises in salinity through the dry season.

So measure at least twice, at opposite ends of the year, and design around the higher figure. A purifier sized to the annual average leaves you unprotected exactly when the supply is worst — which is our standing editorial position and the reason our city pages design to the upper end of the local band rather than its midpoint.

Reading the number

TDS (ppm)	Interpretation	What to buy
Under 50	Very low. Flat taste, minimal mineral content	Nothing, or UV. Do not fit RO
50-150	Ideal for taste and mineral content	UV+UF
150-300	Good. Well within BIS acceptable limits	UV+UF; RO is optional and usually unnecessary
300-500	Acceptable per BIS, but taste may suffer	RO+UV with a TDS controller
500-1,000	Above the BIS acceptable limit of 500	RO+UV, membrane rated 2,000 ppm
1,000-2,000	High. Within the BIS permissible maximum	RO+UV, high-rejection membrane, softening if hard
Above 2,000	Very high. Beyond BIS permissible	RO rated to 3,000 ppm; get a lab analysis first

What a TDS meter cannot tell you — and this is the important part

A TDS meter measures electrical conductivity and converts it to an estimate of dissolved solids. It does not identify what those solids are. Water at 180 ppm of calcium bicarbonate and water at 180 ppm containing arsenic read identically.

That matters because the contaminants with the most serious health consequences in India — arsenic in West Bengal, Bihar, Assam and eastern UP; fluoride across Rajasthan, Gujarat, Telangana and Andhra Pradesh; nitrate in intensively farmed districts; lead from old plumbing — are all invisible to a TDS meter, and all can be present at a completely ordinary reading.

It also tells you nothing about bacteria, which have no meaningful conductivity at all.

Important

If you are on groundwater, or your district has a documented arsenic or fluoride problem, get a NABL-accredited lab test. ₹1,500 answers a question a ₹300 meter is not capable of asking.

Frequently asked questions

How do I check the TDS of water at home?

Buy a digital TDS meter for about ₹300. Run the tap for 30 seconds, collect water in a clean glass at room temperature, immerse the probe to the marked line, stir, and wait 10-20 seconds for the reading to stabilise. Measure the raw supply, not water that has already been filtered.

What is a good TDS level for drinking water?

BIS IS 10500 sets 500 ppm as the acceptable limit and 2,000 ppm as the permissible maximum where no alternative exists. For taste and mineral content, 50-150 ppm is the range most people prefer. Below about 30 ppm the water tastes flat and lacks useful calcium and magnesium.

Can a TDS meter detect contamination?

No, and this is its most important limitation. It measures total dissolved content, not composition. Arsenic, fluoride, nitrate, lead and bacteria can all be present at a perfectly normal TDS reading. For those you need a NABL-accredited lab test costing ₹800-2,500.

Should I measure TDS before or after the purifier?

Both, for different reasons. Measure the raw supply before buying, because that decides which technology you need. Once installed, measure the output every few months — a steadily rising output TDS is the clearest early warning that the RO membrane is failing.

Why does my TDS reading change between seasons?

Because your supply changes. Municipal water is often blended with borewell in summer, tanker supply varies by source, and coastal groundwater grows saltier through the dry season. Measure in both summer and monsoon and design your purifier around the higher reading.