I agree with McL, but public transportation is also an option of course.

Does Rye Playland have any pools or water parks?

Wherever you decide to go, leave early. Beaches, lakes, state parks, etc., get crowded and/or filled up early on hot-weather weekends like this one.
I'd avoid Rye Playland.

What about the pool on the roof of the Parker Meridian? I do love pool swimming and wish there were more alternatives here in Manhattan! You can swim at some city pools when they first open and crowds may not be too bad, especially at the indoor ones.

I think Bear Mountain has a public pool. They're generally pretty skeevy. You just know all of those kids are peeing in it, and you know you're not the only one who has this idea! If you're adventurous what about a water park? Dorney or Camel Beach in PA? Also if you drive out to the Jim Thorpe area in PA you can go to Beltzville Lake which is HUGE and you can swim. It's also always a lot cooler there than here. NYH&R has a private beach in Westchester that I haven't tried, but if you know a member it might be nice.

I hate to rub it in, but I will be by the private pool in a development in PA. For future reference, if you rent a house out in one of the places that has a pool you can use all of the ammenities.

OK, got the idea. I guess adults + pool + cleanliness + close to NY is too much to ask. This was a tough request. Thanks for your ideas.
I may just be forced to go visit some cousins w/rugrats in PA and hang out at their town pool