Don't know what sort of accomodation you are looking for, but we stayed at the Cye Holiday Centre (self catering) in Salou a few years back.
Its far enough away from the main areas to be reasonably quiet but easily accessable (It is about 15 mins walk to the resort Centre & 10 mins to the beach.) I always point out to be careful - there are 2 Cye Apartments in Salou - you need to check out the
Holiday Centre
The Water park is at La Pineda which is another good resort - about 20 mins bus ride from Salou.
Stayed at the Donaire Beach in La Pineda but it was the end of the season when everything was winding down so can't give an idea of what it's like in the high season.
Check out the Hotel revues on this site for some other details.