Text in force at CS27-10: from CS27-0, effective 14 Nov 2003.
For each rotorcraft, with a hull and auxiliary floats, that is to be approved for both taking off from and landing on water, the hull and auxiliary floats must have enough watertight compartments so that, with any single compartment flooded, the buoyancy of the hull and auxiliary floats (and wheel tyres if used) provides a margin of positive stability great enough to minimise the probability of capsizing.
ED Decision 2003/015/RM · Source