On all of the cruises that I have been on, towels have been provided at the pool and then again on the ship for your excursions. You usually have to sign for them with your room key. If they are not returned you are then charged accordingly. However, there are usually bins of towels left unattended at the pool areas, so needless to say I have never went without. On one cruise I even had a cabin attendent pack 2 new towels in my luggage as a Thank You for our generous tip.