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.
Koh Talu is a great choice if you long for white sand beaches and turquoise water relatively near Hua Hin. Famous for coral and turtle conservation projects it also has a good reputation for sustainability.