It's probably a community rule, and as such, can be discussed at the next AGM, and a vote taken on whether to ammend it or not. In the meantime, tell the complainers that rules is rules and to shut up whingeing. Bring their grievance to the next meeting, and just enjoy the damned pool.
(You may guess from this, that I'm fed up with rule breakers and complainers!)
Having said this, each autonomous region of Spain may have it's own by-laws, so you may want to check in case it is actually a law. The administrator of your community should be able to advise you.