the maximum allowable crack width becomes a crucial design consideration to ensure durability and watertightness. According to widely accepted standards like IS 456:2000, the maximum permissible crack width for concrete in continuous contact with water is typically limited to 0.1 mm. This tight control helps prevent leakage, protects embedded reinforcement from corrosion, and maintains the long-term integrity of the structure. For less severe exposure conditions, such as occasional wetting, the limit may be relaxed to around 0.2 mm, and for dry or sheltered environments, up to 0.3 mm may be acceptable. These limits are not just arbitrary—they’re based on extensive research into how cracks influence permeability and the ingress of harmful substances. In practice, achieving these crack width limits involves careful attention to reinforcement detailing, concrete mix design, and construction quality.

Eurocode 2 / EN 1992-3: 0.05–0.20 mm, depending on water pressure vs. wall thickness and required tightness class.

BS 8007: 0.20 mm on water-retaining faces (severe exposure).

ACI 350: 0.25 mm (0.01 in), but leakage can occur if through-cracks exceed ~0.10 mm.

In practice, designers usually adopt 0.20 mm as a safe general limit for water-retaining structures.

Concrete (not hydrophobic) is in principle a permeable material, regardless of whether it has cracks or not. The permissible width of crack opening is usually determined not by water permeability, but by the protection of reinforcement from corrosion. From this point of view, the maximum opening is 0.3 mm. Then everything depends on the purpose of the structure.

Exposure conditions, as international design codes typically impose rigorous limitations, aim to mitigate the ingress of water, chlorides, and other deleterious agents. While the precise value is contingent upon the specific code and exposure classification, a prevalent and stringent stipulation is a crack width not exceeding 0.30 mm (0.012 inches) under service loads, as delineated by Eurocode 2 for structures subjected to seawater or chlorides. In even more aggressive environments, or for structures necessitating a heightened degree of watertightness, such as reservoirs, codes like ACI 318 may mandate a more restrictive threshold of 0.18 mm (0.007 inches).