Chiang Mai has some options for families that needs a good cooling down. No coast but we have waterfalls, rivers, some nice hotel pools and more recently the amount of waterparks are on the increase. Here are some suggestions if you are looking for good waterparks in Chiang Mai.
Phayao is a kind of forgotten, of the beaten track town. It has a pleasant lake and nice mountain scenery. Enjoy local activities in the park at night.