TDS, hardness & what it means · By area

Check the water quality
in your area.

Enter your pincode or city, then tell us whether you're on municipal supply or a borewell. The two are very different numbers — and they point to very different purifiers.

Indicative area readings from government monitoring — not a measurement of your tap.

—Cities mapped
CGWBGovernment monitoring data
500mg/L — BIS acceptable limit
2018–24Monitoring period

Reading

What your TDS number actually means

TDS measures dissolved minerals and salts not bacteria. A low number doesn't mean safe water, and a high number doesn't mean dangerous water. It tells you which kind of treatment fits.

Under 150 mg/L
Excellent

Very low dissolved solids. Naturally soft water, typically from protected lake or hill sources.

UF is the right fit
150 – 300 mg/L
Ideal

Comfortably within limits, with a healthy natural mineral profile. Nothing to remove on TDS grounds.

UF is the right fit
300 – 500 mg/L
Acceptable

Still inside the BIS acceptable limit. Whether you need more than UF depends on hardness and specific contaminants, not TDS alone.

UF or NF
500 – 1,200 mg/L
High

Above the BIS acceptable limit. Treatment recommended to bring dissolved solids down.

NF or RO
Above 1,200 mg/L
Severe

Far above acceptable limits — typically hard groundwater. Reverse osmosis is warranted here.

RO

Bands based on the BIS IS 10500 acceptable limit of 500 mg/L for total dissolved solids, and 2,000 mg/L as the permissible limit where no alternate source exists.

India

Average groundwater TDS, city by city

Central Ground Water Board readings for the area around each city, set against the BIS acceptable limit of 500 mg/L. These are groundwater figures. Where a city runs mainly on treated municipal supply, most large Indian cities do. The number at your tap is usually far lower. Tap any row to check it properly.

City ▲▼ State ▲▼ Groundwater TDS ▼ Main supply ▲▼ Rating ▲▼

Central Ground Water Board readings for the surrounding area, largely EC-derived, from monitoring conducted between 2018 and 2024. The "Main supply" column shows what most households in that city actually receive. For municipal-supplied cities the groundwater figure describes borewell and tanker-fed pockets, not the piped tap — Mumbai is the clearest example, where BMC lake water reaches the tap at roughly 60–190 mg/L against a regional groundwater average of 719.

Match

The purifier your water actually needs

There is no single right purifier. Fitting the technology to your supply matters more than buying the most expensive box and in most low-TDS areas, RO removes minerals you were better off keeping.

Under 300 mg/L

Ultrafiltration

Your water's dissolved solids are already fine. The real risk is microbial — bacteria and cysts picked up in pipelines and building tanks. UF is a physical barrier against those while leaving minerals untouched.

  • 100% mineral retention
  • Zero water wastage
  • Zero electricity
  • FIN Mini
300 – 700 mg/L

Nanofiltration

Sitting around or just above the BIS limit. Nanofiltration reduces dissolved salts and hardness selectively, without stripping water down to nothing the way RO does.

  • Selective salt reduction
  • Retains beneficial minerals
  • Higher recovery than RO
  • FIN UTC — NF 30 / NF 70
Above 700 mg/L

Reverse Osmosis

This is the situation RO was designed for. Dissolved solids are high enough that removing them matters more than retaining minerals — and hardness likely needs handling too.

  • Removes dissolved solids
  • Handles hardness & salinity
  • Test your tap before buying
  • FIN UTC — RO variant

Guidance based on typical area readings. Hardness, fluoride, arsenic and nitrate can each warrant treatment independently of TDS, a lab test of your own supply is the only way to be certain.

Questions

What people ask before buying a purifier
What is a safe TDS level for drinking water in India?
BIS IS 10500 sets 500 mg/L as the acceptable limit for total dissolved solids, and 2,000 mg/L as the permissible limit where no alternate source is available. Below 500 mg/L your water is fine on TDS grounds. Importantly, TDS says nothing about microbial safety — it measures dissolved minerals and salts, not bacteria or viruses.
Is very low TDS a problem?
Water stripped of minerals has its own documented drawbacks. The WHO review of demineralised drinking water recommends a minimum of around 100 mg/L, with roughly 250–500 mg/L considered optimum. This is why fitting RO to already-low-TDS supply is usually the wrong call — you're removing calcium and magnesium you had no reason to lose.
Why does this page show a different number from my TDS meter?
Because they measure different things. The India index shows groundwater readings from government monitoring stations near your area. Your tap is probably fed by treated municipal supply, which is usually much lower. Mumbai is the clearest example: regional groundwater averages around 719 mg/L, but BMC's treated lake water arrives at the tap at roughly 60–190 mg/L. That's why the checker asks which supply you're on before it recommends anything.
Do I need an RO purifier?
Only if your own tap consistently reads above about 500 mg/L, or if hardness, fluoride, arsenic or nitrate exceed BIS limits. Below roughly 300 mg/L, RO is unnecessary and costs you minerals, wasted water and electricity. Between 300 and 500 the answer depends on hardness and specific contaminants rather than TDS alone.
If my water is treated by the municipality, why do I need a purifier at all?
Treatment happens at the plant. Between there and your glass sit kilometres of ageing pipeline and your building's sump and overhead tank. Contamination entering along that route is microbial — bacteria, viruses, cysts, sediment — which is exactly what ultrafiltration removes and what a TDS reading will never show you.
How should I test my own water?
A TDS meter costs very little and gives you an immediate reading — test at the tap you actually drink from, not the tank. For hardness, fluoride, arsenic or nitrate you need a lab test; most cities have NABL-accredited labs that will test a sample cheaply. Test after the monsoon as well, since readings shift seasonally.
Data sources
  • Central Ground Water Board — National groundwater quality monitoring
  • India-WRIS — National Water Informatics Centre
  • Central Pollution Control Board — Water quality criteria
  • BIS IS 10500 — Indian Standard for drinking water (all comparison limits)

Disclaimer: Figures are indicative area estimates drawn from government groundwater monitoring nearest each location and may differ substantially from your exact tap or municipal supply. They are not a substitute for a lab test of your own water. This page is general information, not medical advice, and any product suggestion is general guidance based on typical area readings not a diagnosis of your supply. For health concerns, consult a qualified professional.