The maximum quantity of organic solids permitted in water used in concrete as per IS 456 : 2000 is
Correct Answer: B. 200 mg/l
📚 Detailed Explanation: Organic Solids Limit in Mixing Water (IS 456)
Organic matter in mixing water can interfere with cement hydration, retard setting, reduce strength, and introduce air bubbles into the concrete. IS 456:2000 specifies a strict numerical limit on organic solids to control these effects.
Why B (200 mg/l) is correct: IS 456:2000 Clause 5.4 Table 1 specifies the following limits for mixing water: Organic solids ≤200 mg/l. This is the single most tested specific value from this clause. The other options (100, 300, 400 mg/l) are all incorrect. The 200 mg/l limit applies to the total dissolved organic material; water with higher levels must be treated or rejected.
IS 456:2000 Water Quality Limits (Table 1)
| Impurity | Maximum (mg/l) |
|---|---|
| Organic solids | 200 |
| Inorganic solids | 3000 |
| Sulphates (as SO3) | 400 |
| Chlorides (RCC) | 500 |
| Chlorides (plain concrete) | 2000 |
| Suspended matter | 2000 |
Key Concepts for Students
- 200 mg/l for organic solids — this is the most frequently tested specific value from IS 456 water quality requirements.
- Organic matter (humic acids, tannins from vegetation) retards hydration and can cause false set or weak cement paste.
- A simple field test: water passing the mortar-cube strength test (not less than 90% of cubes made with distilled water) is acceptable per IS 456.