Get real. Unless you're 12-going-on-13, the only place that promises around-the-clock cool is a seat that faces the window unit. But for those who insist on getting out into the summer sun without baking, Arlington's newest water park is hard to beat. Think a day at the beach with a little Disneyland thrown in--or as one comedian put it, you can think of it as a ride on the enema express.