5.7 : Quality of Water

In concrete preparation, the quality of water is paramount as it affects the strength and durability of the concrete. Potable water is usually preferred; however, it must not have excessive sodium or potassium to prevent compromising the concrete's integrity. Water quality is typically evaluated based on impurities such as dissolved solids, chlorides, and sulfates, and its pH value is ideally between 6 and 8. Even slightly acidic natural water may be acceptable unless it contains harmful organic matter or algae, which could adversely affect the concrete's properties. The permissible limits for these impurities vary as per different standards like BS 3148:1980, BS EN 1008:2002 and ASTM C 1602–06. Silt content, if high, can be mitigated by allowing the water to stand in a settling basin, and wash water from concrete mixers can be reused if clean. Although potable water can also be suitable for curing, it's crucial that curing water lacks impurities like free carbon dioxide, which can erode hardened concrete, and iron or organic matter that may cause staining. The use of seawater, while considered for regions with freshwater scarcity, poses risks like reinforcement corrosion and efflorescence, thereby being generally inadvisable for mixing or curing. Thus, while water quality requirements for concrete mixing and curing are stringent, some flexibility exists based on the concrete application and environmental considerations.