The reported study looked at the effect of reducing free water contents, and thereby binder contents, on the ingress of chloride in concrete. Concretes with equal water/binder ratio (and design strength), but with water contents reduced by up to 30 litres/m3, were tested for chloride diffusion (D) and penetration. The quality of the microstructure was inferred from initial surface absorption tests (ISAT). The results show no practical difference in chloride durability between the corresponding concretes, and that reducing the binder content, (providing that the water/binder ratio is maintained) is not likely to be detrimental. However, the results reported underline the importance of binder type, in this case PFA. Implications of the results are discussed and, in light of the findings, whether specifications which demand minimum cement contents are justified.