South Germantown Recreational Park Splash Park is open daily through September 1, from 10 to 8pm. Directions (and pictures) are on the website.

Cost: $3.50 per person. Discount Book of 10 tickets for $31. Group rate (31+) per ticket $2.80.

From the website:

Kids enjoy playing underneath the massive waterfall and trying to guess which tumbling bucket will tip over next. There is also a rain tree, a water tunnel, and a 36′ water maze 280 ground-level jets shoot forth 6,000 gallons of water per minute for the ultimate in hot-weather relief. Lockers and cubbies, showers, dressing room, restrooms and a vending area are located nearby. Fully accessible and all ages are welcome.

Also at this park is a wonderful (free) section called Adventure Playland. Directions (and pictures) here.

From the website:

South Germantown Recreational Park Adventure Playland is located at 17920 Germantown Park Drive in Germantown. Among the many activities for children at South Germantown Recreational Park, Adventure Playland is a favorite. In addition to the playground equipment, the park features ball fields and picnic area. Shelters (about 200 yards past the playground) are available for rent.