Late May or early September is the sweet spot.

May is usually warm enough for water play in most climates, and crowds are thin because school is still in session. Early September works too — kids are back in school, the weather is often still hot, and you avoid the holiday weekend rush.

The exact month depends on where you are. If you’re in a northern state, late June might still be fine, but that’s when the summer crowds start. The key is to avoid the July 4–Labor Day peak. Aim for a window when the water is warm but the lines are short.

Late May is usually the safer bet for both warmth and emptiness. Just check the local pool or park’s opening schedule — some don’t turn on the spray until Memorial Day weekend.

Don’t bother going in April unless you’re in Florida.