That's why we use the %fill of an Olympic Sized Pool - doesn't matter from what continent the field comes, they fill the pool equally.

Aren't there significant differences in allowed depth (from minimum of 2m to maximum of 3m)?

Good catch. We've run into a problem somewhere along this journey of comparing the compression strength of a snails tooth to the tensile strength of a spiders web.

So a snail's tooth can only hold a 2m deep worth of Olympic pool (sea)water, but it breaks before you get to a 3m deep pool.