--- title: "Water fit for drinking; test on water" subject: "Concrete Technology and Masonry Structure" chapter: 1 key: "semester_5/concrete_technology_and_masonry_structure:water-fit-for-drinking" source: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/water-fit-for-drinking site: BCT Engineering --- # Water fit for drinking; test on water Concrete Technology and Masonry Structure · Chapter 1: Introduction to concrete and concrete materials - Asked in: 2082 Baisakh, 4+2 marks - Video: [Water Quality test for Construction work Asper IS :3025 pH/TDS/ Alkalinity/acidity/Organic/So4/Cl](https://www.youtube.com/watch?v=kKrMSiQWi30) — Crazy Civil Engineering - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/water-fit-for-drinking - Whole chapter: https://www.bctengineer.com/md/semester_5/concrete_technology_and_masonry_structure/chapter-1 ## Question "In many specifications, quality of water is covered by a clause saying that water should be fit for drinking." Explain. Is there any standard test on water? What are the functions of water in a concrete mix? ## Short answer Potable water is deemed suitable because experience shows harmless impurity levels, avoiding special tests. Standard tests include chemical limits (pH≥6, sulphates≤400 mg/L, chlorides≤500 mg/L for RCC) and physical comparison (strength≥90% of distilled water mix, setting time ±30 min). Water hydrates cement, provides workability, and is used for curing. ## Answer #### "Water should be fit for drinking" IS 456:2000 cl. 5.4 says that water used for mixing and curing should be clean and free from injurious amounts of oils, acids, alkalis, sugar, salts, organic materials and other substances harmful to concrete or steel. **Potable (drinking) water** is regarded as suitable because long experience has shown that it contains only acceptable amounts of these impurities, so it needs no special testing. But the reverse is not always true: some water that is not fit to drink (e.g. slightly salty or with a bad smell) may still be fine for concrete, while sweet-tasting water containing sugar, or water with high sulphates, may not be suitable. The clause is therefore a simple, practical guide. Sea water is not allowed in RCC, and water with a pH below 6 is unsuitable. #### Standard tests on water (IS 456 cl. 5.4, IS 3025) - **Chemical tests**: pH (not less than 6), organic solids (max 200 mg/L), inorganic solids (3000 mg/L), sulphates as SO$_3$ (400 mg/L), chlorides (2000 mg/L for plain concrete; 500 mg/L for RCC), suspended matter (2000 mg/L). - **Physical comparison tests**: the average 28-day compressive strength of three 150 mm cubes made with the test water should be not less than 90% of that of cubes made with distilled water, and the initial setting time should not differ by more than ± 30 min and should not be less than 30 min. - Acid test: 200 mL of the sample should need not more than 2 mL of 0.1 N NaOH to neutralise it, using phenolphthalein; alkalinity test: not more than 10 mL of 0.1 N HCl, using methyl orange. #### Functions of water in a concrete mix 1. Reacts with cement (hydration) to form the binding gel. 2. Acts as a lubricant, giving workability for mixing, placing and compaction. 3. Used in curing to keep hydration going and to control shrinkage and heat. 4. Washes the aggregates and helps the bonding of paste and aggregate. 5. Excess water, however, evaporates and leaves pores that decrease strength, so the w/c ratio must be controlled. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Why do specifications ask for water fit for drinking? A. Only drinking water can hydrate cement B. Potable water is known by experience to have acceptable levels of harmful impurities, so no special testing is needed C. Drinking water is tested for every concrete batch D. Non-potable water is always forbidden Answer: B. Long experience shows potable water contains acceptable impurity levels, making the clause a simple practical guide. (Key point: Why potable water is specified) 2. Which statement about the potable-water clause is correct? A. Sweet-tasting water with sugar is always suitable B. Water not fit to drink may still be fine for concrete, but water with sugar or high sulphates may be unsuitable C. All water not fit to drink is unsuitable D. Sea water is allowed in RCC Answer: B. The reverse is not always true: slightly salty water can be fine, while sugar or high sulphates harm concrete. (Key point: Converse not always true) 3. In the comparison test, test water cubes at 28 days should give strength of at least: A. 50% of distilled water cubes B. 75% of distilled water cubes C. 100% of distilled water cubes D. 90% of distilled water cubes Answer: D. Average 28-day strength of three 150 mm cubes must be not less than 90% of that with distilled water. (Key point: Physical comparison test) 4. Why must the w/c ratio be controlled even though water gives workability? A. Excess water evaporates leaving pores that decrease strength B. Excess water increases cement hydration beyond need C. Water reacts with aggregate D. Water makes cement set faster Answer: A. Surplus water evaporates leaving pores, reducing strength. 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