Most hotels are now becoming much stricter with regard to non-residents using their pool. They have realised they can make extra money! Most hotels will allow you to use their pool but will charge approx Rs100 per day - (if you use the pool for only a few hours you still have to pay the full amount). They will ask for your room number when you order drinks and, yes, they will check. Best way is to just walk in, speak to one of the waiters, they will keep quiet for just a few rupees tip when you leave.
Yes, the sea is very warm but do be careful of the strong current along Calangute/Candolim beaches. It is great when the waves are breaking, but not so great when you get dragged under with the current. If you are not a strong swimmer, it is best to stay to say in shallow water when the waves are high or the. tide is changing
Please don't be put off by this information, mostly the sea is very calm but I do think that tourists should be aware of this and am always surprised that this is not mentioned by tour operators.
Also, did you know that Goa is a NON SMOKING STATE?