Chemical Parameters for Drinking Water (IS 10500 Standards)
Water quality assessment is essential to ensure safety for human consumption and aquatic health. Chemical parameters of drinking water refer to the physical-chemical composition, dissolved salts, heavy metals, and gaseous components present in water. In India, the Bureau of Indian Standards (BIS) prescribes drinking water specifications under IS 10500:2012 (aligning with WHO guidelines).
Key Chemical Parameters and Permissible Limits
The following table summarizes the essential chemical parameters, their maximum acceptable/permissible limits as per IS 10500, and their biological significance:
| Chemical Parameter | Acceptable Limit (Max) | Permissible Limit (in absence of alternate source) | Health & Environmental Significance |
|---|---|---|---|
| pH Value | 6.5 – 8.5 | No Relaxation | Low pH causes pipe corrosion and metal dissolution; high pH causes incrustation and bitter taste. |
| Total Dissolved Solids (TDS) | $500 \text{ mg/L}$ | $2000 \text{ mg/L}$ | Measures inorganic salts ($\text{Ca}^{2+}$, $\text{Mg}^{2+}$, $\text{Na}^+$, $\text{Cl}^-$). High TDS affects palatability and causes gastrointestinal irritation. |
| Total Hardness ($\text{as CaCO}_3$) | $200 \text{ mg/L}$ | $600 \text{ mg/L}$ | Caused by $\text{Ca}^{2+}$ and $\text{Mg}^{2+}$ ions. Causes scaling in boilers and reduced soap lathering. |
| Chlorides ($\text{Cl}^-$) | $250 \text{ mg/L}$ | $1000 \text{ mg/L}$ | High concentrations impart a salty taste and indicate sewage contamination or industrial pollution. |
| Sulfates ($\text{SO}_4^{2-}$) | $200 \text{ mg/L}$ | $400 \text{ mg/L}$ | Excessive sulfate levels when combined with magnesium produce a laxative effect on humans. |
| Nitrates ($\text{NO}_3^-$) | $45 \text{ mg/L}$ | No Relaxation | High nitrates cause Methemoglobinemia (Blue Baby Syndrome) in infants due to reduced blood oxygen carrying capacity. |
| Fluorides ($\text{F}^-$) | $1.0 \text{ mg/L}$ | $1.5 \text{ mg/L}$ | $<0.5 \text{ mg/L}$ leads to dental caries; $>1.5 \text{ mg/L}$ causes Dental & Skeletal Fluorosis. |
| Dissolved Oxygen (DO) | $> 4\text{--}6 \text{ mg/L}$ | — | Indicates aquatic life sustainability and water freshness. Low DO signifies high organic pollution (BOD/COD). |
| Lead ($\text{Pb}$) | $0.01 \text{ mg/L}$ | No Relaxation | Toxic cumulative heavy metal; causes neurological damage and kidney dysfunction. |
Analytical Techniques for Water Testing (M.Sc. Exam Special)
- EDTA Complexometric Titration: Used to determine Total, Permanent, and Temporary Hardness of water using Eriochrome Black T (EBT) indicator at $\text{pH } 10$.
- Mohr's Method (Argentometric Titration): Used for determination of chloride ions ($\text{Cl}^-$) by titrating against standard $\text{AgNO}_3$ solution using $\text{K}_2\text{CrO}_4$ as indicator.
- Winkler’s Method: Classical iodometric titration procedure used to determine Dissolved Oxygen (DO) levels in environmental samples.
- Spectrophotometry & Flame Photometry: Used for trace determination of toxic heavy metals ($\text{Pb}$, $\text{As}$, $\text{Cd}$) and alkali metals ($\text{Na}^+$, $\text{K}^+$).
Test Your Understanding: Water Chemistry MCQs
1. Excess concentration of nitrates ($>45 \text{ mg/L}$) in drinking water causes which health condition in infants?
A) Skeletal Fluorosis
B) Methemoglobinemia (Blue Baby Syndrome)
C) Minamata Disease
D) Dental Caries
View Answer
Correct Answer: B) Methemoglobinemia (Blue Baby Syndrome)
Explanation: Nitrates are reduced to nitrites in the infant digestive tract, binding to hemoglobin and forming methemoglobin, which reduces oxygen transport capacity.
Explanation: Nitrates are reduced to nitrites in the infant digestive tract, binding to hemoglobin and forming methemoglobin, which reduces oxygen transport capacity.
2. Which indicator is commonly used in the complexometric determination of total water hardness using EDTA at pH 10?
A) Phenolphthalein
B) Potassium Chromate
C) Eriochrome Black T (EBT)
D) Methyl Orange
View Answer
Correct Answer: C) Eriochrome Black T (EBT)
Explanation: EBT forms a wine-red complex with $\text{Ca}^{2+}$ and $\text{Mg}^{2+}$ ions at $\text{pH } 10$, turning steel blue at the EDTA equivalence end-point.
Explanation: EBT forms a wine-red complex with $\text{Ca}^{2+}$ and $\text{Mg}^{2+}$ ions at $\text{pH } 10$, turning steel blue at the EDTA equivalence end-point.
3. As per IS 10500 standards, what is the maximum permissible limit for Fluorides in drinking water?
A) $0.5 \text{ mg/L}$
B) $1.5 \text{ mg/L}$
C) $3.0 \text{ mg/L}$
D) $5.0 \text{ mg/L}$
View Answer
Correct Answer: B) 1.5 mg/L
Explanation: The acceptable limit is $1.0 \text{ mg/L}$ and the upper permissible limit in the absence of an alternate water source is $1.5 \text{ mg/L}$.
Explanation: The acceptable limit is $1.0 \text{ mg/L}$ and the upper permissible limit in the absence of an alternate water source is $1.5 \text{ mg/L}$.