The Puerto Azul will let you use their pool, but at a price, They will charge for a morning and afternoon say, at a set fee, which includes lunch and a drink, and also an evening package including a meal and drink. I cannot remember the price exactly, but was in region of 20 Euro each.
We had 9 family members staying there last year, but not us. I spoke nicely to them and we were able to visit for free. Lunch is exceptional good value too.
Also, some years ago stayed in Hostal Bahia {twice} and The Capri, and because they were part of the Hoposa Group, we were allowed to use the Daina pool at any time free of charge,
We have, over the years, had many a drink and snacks, in a very wide range of Hotels in PP, and were never challenged about where we were staying - it is the hospitality business after all!!