Water quality guide
What a water report measures: TDS, hardness and the BIS limits
A water report is more than a TDS number. This page says what each parameter is, why it matters, and the two limits India’s drinking-water standard sets for it.
Source: Bureau of Indian Standards, IS 10500:2012 with Amendment No. 1 (2015).
Acceptable and permissible: how the two limits work
India's drinking-water standard, IS 10500:2012 from the Bureau of Indian Standards, gives two numbers for most parameters: an acceptable limit, and a permissible limit in the absence of an alternate source.
The standard recommends that the acceptable limit be implemented. Water above it is rendered not suitable, but may still be tolerated up to the permissible limit where there is no alternative source. Above the permissible limit, the standard says the source will have to be rejected.
Where the permissible column says no relaxation, the acceptable limit is the only limit: nitrate, arsenic and iron are examples.
Source: IS 10500:2012 Drinking Water Specification, with Amendment No. 1 (2015), Bureau of Indian Standards.
The limits at a glance
Acceptable limit, and the permissible limit where there is no alternate source.
| Parameter | Acceptable | Permissible |
|---|---|---|
| Total dissolved solids (TDS)mg/L | 500 | 2,000 |
| Total hardnessmg/L as CaCO₃ | 200 | 600 |
| Fluoridemg/L | 1.0 | 1.5 |
| Nitratemg/L as NO₃ | 45 | No relaxation |
| Arsenicmg/L | 0.01 | No relaxation |
| Ironmg/L | 1.0 | No relaxation |
Total dissolved solids (TDS)
The total weight of minerals and salts dissolved in a litre of water: calcium, magnesium, sodium, bicarbonates, chlorides, sulphates and others. It is a single number for how mineral-laden water is, not a measure of any one contaminant.
- BIS acceptable limit
- 500 mg/L
- Permissible, no alternate source
- 2,000 mg/L
Why it matters
High TDS makes water taste salty or bitter and leaves scale; it also signals that individual salts and minerals are worth testing. TDS says nothing about bacteria.
Of the 74 cities mapped here, 46 record average groundwater TDS above the 500 mg/L acceptable limit. The city reports band TDS like this:
- ExcellentUnder 150 mg/L
- Ideal150–299 mg/L
- Acceptable300–499 mg/L
- High500–1,199 mg/L
- Severe1,200–1,999 mg/L
- Extreme2,000+ mg/L
The bands are this site’s reading aid; the 500 and 2,000 mg/L lines are the standard’s. TDS in drinking water: what is a safe level?
Flagged in 49 of the 74 city reports
and 37 more on the India Water Quality Index.
Total hardness
The calcium and magnesium dissolved in water, expressed as an equivalent weight of calcium carbonate. Hardness is one part of TDS.
- BIS acceptable limit
- 200 mg/L as CaCO₃
- Permissible, no alternate source
- 600 mg/L as CaCO₃
Why it matters
Scaling on taps, geysers and appliances.
30 of the city reports carry a measured hardness figure; 25 of those are above the 200 mg/L acceptable limit.
Flagged in 29 of the 74 city reports
and 17 more on the India Water Quality Index.
Nitrate
A nitrogen compound that reaches groundwater from fertiliser, sewage and animal waste.
- BIS acceptable limit
- 45 mg/L as NO₃
- Permissible, no alternate source
- No relaxation
Why it matters
Risky for infants (blue-baby syndrome).
Flagged in 16 of the 74 city reports
and 4 more on the India Water Quality Index.
Arsenic
A toxic element that occurs naturally in some aquifers.
- BIS acceptable limit
- 0.01 mg/L
- Permissible, no alternate source
- No relaxation
Why it matters
Toxic; long-term exposure is carcinogenic.
Flagged in 1 of the 74 city reports
Iron
Dissolved iron from iron-bearing rock and soil, and from old iron pipes.
- BIS acceptable limit
- 1.0 mg/L
- Permissible, no alternate source
- No relaxation
Why it matters
Metallic taste, staining of fixtures and clothes.
Flagged in 4 of the 74 city reports
Water parameters: questions
What is TDS in water?
TDS, total dissolved solids, is the combined weight of minerals and salts dissolved in a litre of water, measured in milligrams per litre (mg/L). India's BIS IS 10500 standard sets an acceptable limit of 500 mg/L and a permissible limit of 2,000 mg/L where no alternate source exists.
What is the BIS limit for TDS in drinking water?
500 mg/L is the acceptable limit in IS 10500:2012, and 2,000 mg/L is the permissible limit in the absence of an alternate source. The standard recommends implementing the acceptable limit, and says a source above the permissible limit will have to be rejected.
What is the difference between TDS and hardness?
Hardness is the calcium and magnesium in water, expressed as calcium carbonate; TDS is everything dissolved, hardness included. Water can have high TDS from sodium salts and still be soft. BIS sets hardness at 200 mg/L acceptable and 600 mg/L permissible, against 500 and 2,000 mg/L for TDS.
What are the BIS limits for fluoride, nitrate and arsenic?
Fluoride: 1.0 mg/L acceptable, 1.5 mg/L permissible. Nitrate: 45 mg/L, with no relaxation. Arsenic: 0.01 mg/L, with no relaxation since Amendment No. 1 of 2015. All three are from IS 10500:2012.
Does a low TDS reading mean water is safe to drink?
No. TDS measures dissolved minerals and salts only. It says nothing about bacteria, and it does not single out fluoride, nitrate or arsenic, each of which has its own limit in IS 10500 and needs its own test.
Source
IS 10500:2012 Drinking Water Specification, with Amendment No. 1 (2015), Bureau of Indian Standards, Tables 1 to 3. City flags are from Central Ground Water Board reports, listed on each city page.
Limits are for drinking water as supplied. City figures are area-level groundwater readings, not a measurement of your tap. This page is general information, not medical advice.