The water we get in Hua Hin comes from private wells which may called “hard” water since it often has a lot of Calcium. If a house is connected to the city water from Hua Hin, it comes from the Pranburi water dam. This water is refined and has only a small amount of calcium. Thee is a good review on Hua Hin water to read here: https://tinyurl.com/yzprkw7c
The monthly costs are documented on the PWA website https://en.pwa.co.th and can be found in this table: