# Drinking Water and Air Quality Standards for NEET PG PSM: IS 10500 Limits, Coliforms, Residual Chlorine, NAAQS 2009

Source: https://tracknation.in/story/drinking-water-and-air-quality-standards-for-neet-pg-psm-is-10500-limits-coliforms-residual-chlorine-naaqs-2009 (TrackNation — free UPSC notes with PYQs)

> NEET PG Community Medicine: India's drinking-water standard IS 10500:2012 — acceptable vs permissible limits for pH, turbidity, TDS, hardness, fluoride, nitrate, iron and arsenic; the bacteriological standard (no E. coli or coliform in any 100 ml); free residual chlorine 0.2/0.5 mg/l and what chlorination cannot kill — plus the 12 pollutants of the National Ambient Air Quality Standards 2009. From the official standards, with verified MCQs, memory hooks and cards.

## Start Here

🎯 **Exam priority: Medium.** *Environment questions in PSM lean on numbers: drinking-water limits, the coliform standard,
residual chlorine and air-quality standards. Everything here is from India's official standards — **BIS IS 10500:2012** and the
**CPCB National Ambient Air Quality Standards (2009)**.*

CBME mapping: **CM 3** (environment and health).

## Drinking Water: Acceptable vs Permissible

- IS 10500 gives an **acceptable limit** (to be implemented) and a **permissible limit in the absence of an alternate
source**; above the permissible limit the source has to be **rejected**.

- The standard notes that India's water-quality problems are led by **excess iron**, then fluoride, salinity, nitrate and
arsenic.

| **Parameter (IS 10500:2012)**

 | **Acceptable limit**

 | **Permissible (no alternate source)**

 |
| pH

 | 6.5–8.5

 | no relaxation

 |
| Turbidity (NTU)

 | 1

 | 5

 |
| Total dissolved solids (mg/l)

 | 500

 | 2000

 |
| Total hardness as CaCO₃ (mg/l)

 | 200

 | 600

 |
| Calcium (mg/l)

 | 75

 | 200

 |
| Chloride (mg/l)

 | 250

 | 1000

 |
| Sulphate (mg/l)

 | 200

 | 400

 |
| Fluoride (mg/l)

 | 1.0

 | 1.5

 |
| Nitrate as NO₃ (mg/l)

 | 45

 | no relaxation

 |
| Iron (mg/l)

 | 0.3

 | no relaxation

 |
| Arsenic (mg/l)

 | 0.01

 | 0.05

 |
| Lead (mg/l)

 | 0.01

 | no relaxation

 |
| Free residual chlorine (mg/l, minimum)

 | 0.2

 | 1

 |

## Bacteriological Standard

- **All drinking water**: *E. coli* or thermotolerant coliforms must **not be detectable in any 100 ml**.
Treated water entering or in the distribution system must also have **no total coliforms in any 100 ml**.

- ***E. coli* is the more precise indicator of faecal pollution**; thermotolerant coliforms are an acceptable
alternative. Total coliforms are *not* acceptable indicators of the sanitary quality of rural supplies in the tropics.

- If coliforms are found, act immediately — at the least, **repeat the sample**; if positive again, investigate the cause.

## Chlorination: What It Does and Doesn't Do

- **Free residual chlorine** (tested at the consumer end, only if the water is chlorinated): at least **0.2 mg/l**;
at least **0.5 mg/l** when protection against viral infection is needed.

- In practice, **more than 0.5 mg/l of free chlorine for 1 hour** inactivates viruses.

- Normal chlorine doses are **ineffective against amoebic cysts** — they are removed only by effective filtration.
*Cryptosporidium* and *Giardia* are chlorine-resistant too.

## Ambient Air Quality Standards (NAAQS 2009)

Notified by the CPCB on **18 November 2009** under the Air (Prevention and Control of Pollution) Act, 1981 — **12
pollutants**. The same values apply to industrial, residential, rural and other areas, except stricter annual SO₂ and NO₂ in
ecologically sensitive areas.

| **Pollutant (unit)**

 | **Annual**

 | **24 hours**

 | **Shorter averages**

 |
| SO₂ (µg/m³)

 | 50 (20 in ecologically sensitive areas)

 | 80

 | —

 |
| NO₂ (µg/m³)

 | 40 (30 in ecologically sensitive areas)

 | 80

 | —

 |
| PM₁₀ (µg/m³)

 | 60

 | 100

 | —

 |
| PM₂.₅ (µg/m³)

 | 40

 | 60

 | —

 |
| Ozone (µg/m³)

 | —

 | —

 | 8 h: 100 · 1 h: 180

 |
| Lead (µg/m³)

 | 0.50

 | 1.0

 | —

 |
| CO (mg/m³)

 | —

 | —

 | 8 h: 2 · 1 h: 4

 |
| Ammonia (µg/m³)

 | 100

 | 400

 | —

 |
| Benzene (µg/m³)

 | 5

 | —

 | —

 |
| Benzo(a)pyrene (ng/m³)

 | 1

 | —

 | —

 |
| Arsenic (ng/m³)

 | 6

 | —

 | —

 |
| Nickel (ng/m³)

 | 20

 | —

 | —

 |

- **Annual** value = arithmetic mean of at least **104** measurements a year (twice a week, 24-hourly).

- 24-, 8- and 1-hour values must be met **98% of the time**; they may be exceeded 2% of the time, but not on two consecutive
monitoring days.

## Traps the Examiner Sets

- Fluoride: acceptable **1.0**, permissible **1.5** mg/l. Nitrate **45** mg/l with no relaxation.

- Arsenic: 0.01 (acceptable) / 0.05 (permissible) mg/l.

- Coliforms: **zero in any 100 ml** — not "less than 10".

- Residual chlorine minimum 0.2 mg/l; 0.5 mg/l for viral protection.

- Chlorination does not kill amoebic cysts — filtration does.

- PM₂.₅ 24-hour standard is **60** µg/m³; PM₁₀ 24-hour is **100**. CO is in **mg**/m³.

## Memory Hooks & Shortcuts

*Shortcuts to lock in this article's numbers and lists. Each one only re-packages facts proven above.*

- 🧠 **One-and-a-half for fluoride** — 1.0 acceptable, 1.5 permissible mg/l

- 🧠 **Forty-five for nitrate, no excuses** — nitrate 45 mg/l with no relaxation

- 🧠 **Zero in a hundred** — no E. coli or coliform in any 100 ml

- 🧠 **Point-two to stay safe, point-five for viruses** — residual chlorine 0.2 mg/l minimum; 0.5 mg/l for viral protection; > 0.5 for 1 h kills viruses

- 🧠 **Chlorine can't crack cysts** — amoebic cysts need filtration; Cryptosporidium and Giardia resist chlorine

- 🧠 **PM: 60–100 and 40–60** — PM₁₀ annual 60, 24 h 100; PM₂.₅ annual 40, 24 h 60

## Rapid-Revision Cards

- Acceptable = to implement; permissible only if no alternate source; above it, reject the source.

- 1.0 acceptable / 1.5 permissible mg/l.

- 45 mg/l as NO₃, no relaxation.

- 0.01 / 0.05 mg/l.

- 500 / 2000 · 200 / 600 mg/l.

- 6.5–8.5 (no relaxation) · 1 / 5 NTU.

- 0.3 and 0.01 mg/l — no relaxation.

- E. coli / thermotolerant coliforms: none in any 100 ml.

- E. coli.

- ≥ 0.2 mg/l at consumer end; ≥ 0.5 for viral protection.

- > 0.5 mg/l free chlorine for 1 hour.

- Amoebic cysts (filter); Cryptosporidium, Giardia resistant.

- 12 pollutants; notified 18 Nov 2009 under the Air Act 1981.

- PM₁₀ 60 / 100; PM₂.₅ 40 / 60 µg/m³ (annual / 24 h).

- O₃ 100 (8 h), 180 (1 h) µg/m³ · CO 2 (8 h), 4 (1 h) mg/m³.

- 98% of the time; annual mean from ≥ 104 measurements.

## Sources

## Sources

*Facts in this article were checked against these documents.*

- IS 10500:2012 Drinking Water — Specification (Second Revision) — Bureau of Indian Standards, 2012 (link)

- National Ambient Air Quality Standards (Notification of 18 November 2009) — Central Pollution Control Board, 2009 (link)

## Test Yourself: Practice Questions

Sixteen questions in NEET PG style.

## Practice Questions (NEET PG pattern)

*Original questions written in the style of the exam: +4 for a correct answer, −1 for a wrong one. Every answer
was checked against the sources listed above. NEET PG papers are not published by NBEMS, so these are not past-paper questions.*

**Q1.** Under IS 10500:2012, the acceptable limit of fluoride in drinking water is

- (a) 1.0 mg/l

- (b) 1.5 mg/l

- (c) 2.0 mg/l

- (d) 0.5 mg/l

**Answer: (a)** — Acceptable 1.0 mg/l; permissible (no alternate source) 1.5 mg/l.

**Q2.** The maximum nitrate (as NO₃) in drinking water per IS 10500 is

- (a) 45 mg/l, with no relaxation

- (b) 10 mg/l

- (c) 45 mg/l, relaxable to 100

- (d) 100 mg/l

**Answer: (a)** — Nitrate 45 mg/l — no relaxation.

**Q3.** The bacteriological standard for drinking water is that E. coli or thermotolerant coliforms

- (a) are absent in 95% of samples

- (b) are fewer than 1 per ml

- (c) are fewer than 10 per 100 ml

- (d) are not detectable in any 100 ml sample

**Answer: (d)** — E. coli/thermotolerant coliforms: not detectable in any 100 ml; total coliforms also absent in treated water.

**Q4.** The most precise indicator of faecal pollution of drinking water is

- (a) total coliforms

- (b) E. coli

- (c) faecal streptococci

- (d) Clostridium perfringens

**Answer: (b)** — E. coli is the more precise indicator; thermotolerant coliforms are an acceptable alternative.

**Q5.** The minimum free residual chlorine at the consumer end of a chlorinated supply is

- (a) 0.5 mg/l

- (b) 1.0 mg/l

- (c) 0.2 mg/l

- (d) 2.0 mg/l

**Answer: (c)** — At least 0.2 mg/l; at least 0.5 mg/l when protection against viral infection is required.

**Q6.** When protection against viral infection is required, free residual chlorine should be at least

- (a) 0.1 mg/l

- (b) 0.5 mg/l

- (c) 5 mg/l

- (d) 0.2 mg/l

**Answer: (b)** — IS 10500: minimum 0.5 mg/l for viral protection; > 0.5 mg/l for 1 hour inactivates viruses.

**Q7.** Which is NOT reliably killed by chlorination at the doses used in waterworks?

- (a) Vibrio cholerae

- (b) Amoebic cysts

- (c) E. coli

- (d) Salmonella Typhi

**Answer: (b)** — Chlorination is ineffective against amoebic cysts; only effective filtration removes them.

**Q8.** If the iron content of drinking water exceeds 0.3 mg/l under IS 10500:2012

- (a) there is no relaxation — the acceptable limit is the limit

- (b) it may be accepted up to 1.0 mg/l

- (c) it is ignored if TDS is normal

- (d) it is permissible up to 3 mg/l

**Answer: (a)** — Iron 0.3 mg/l, no relaxation.

**Q9.** The permissible limit of total dissolved solids in the absence of an alternate source is

- (a) 1500 mg/l

- (b) 1000 mg/l

- (c) 500 mg/l

- (d) 2000 mg/l

**Answer: (d)** — TDS acceptable 500, permissible 2000 mg/l.

**Q10.** The acceptable limit of turbidity in drinking water is

- (a) 10 NTU

- (b) 1 NTU

- (c) 5 NTU

- (d) 25 NTU

**Answer: (b)** — Turbidity acceptable 1 NTU; permissible 5 NTU.

**Q11.** Arsenic in drinking water: acceptable / permissible limits under IS 10500:2012 are

- (a) 0.001 / 0.01 mg/l

- (b) 0.05 / 0.1 mg/l

- (c) 0.01 / 0.05 mg/l

- (d) 0.1 / 0.5 mg/l

**Answer: (c)** — Total arsenic 0.01 mg/l acceptable, 0.05 mg/l permissible.

**Q12.** How many pollutants are covered by India's National Ambient Air Quality Standards (2009)?

- (a) 10

- (b) 12

- (c) 8

- (d) 6

**Answer: (b)** — 12: SO₂, NO₂, PM₁₀, PM₂.₅, O₃, Pb, CO, NH₃, benzene, benzo(b)pyrene, arsenic, nickel.

**Q13.** The 24-hour NAAQS for PM₂.₅ is

- (a) 25 µg/m³

- (b) 60 µg/m³

- (c) 40 µg/m³

- (d) 100 µg/m³

**Answer: (b)** — PM₂.₅: annual 40, 24-hour 60 µg/m³; PM₁₀: annual 60, 24-hour 100.

**Q14.** Which NAAQS value is lower in ecologically sensitive areas than in other areas?

- (a) Annual lead

- (b) 24-hour PM₁₀

- (c) Annual SO₂ (20 vs 50 µg/m³)

- (d) 8-hour ozone

**Answer: (c)** — Annual SO₂ 20 and NO₂ 30 µg/m³ in ecologically sensitive areas; all others are the same.

**Q15.** Under NAAQS, 24-hourly standards must be complied with for what share of the year?

- (a) 100%

- (b) 98%

- (c) 90%

- (d) 95%

**Answer: (b)** — 98% of the time; 2% exceedance allowed, but not on two consecutive monitoring days.

**Q16.** The NAAQS unit for carbon monoxide is

- (a) ng/m³ (annual 20)

- (b) µg/m³ (8 h: 100)

- (c) ppm (annual 9)

- (d) mg/m³ (8 h: 2; 1 h: 4)

**Answer: (d)** — CO is the only NAAQS pollutant expressed in mg/m³: 2 (8-hour) and 4 (1-hour).

### Active Recall

From memory: explain acceptable vs permissible limits and give the IS 10500 values for pH, turbidity, TDS, fluoride, nitrate, iron and arsenic; state the bacteriological standard and the residual-chlorine rules, and what chlorination cannot kill; then list the NAAQS pollutants with the PM and gas standards and the compliance rule.