Getting drinking water is extremely easy in Chiang Mai, Thailand. Here in Saigon (where I’m staying now), I have to go to Circle K, Family Mart, or some other convenience store everytime I want to buy more water. In Chiang Mai, however, they have water dispensers scattered across the entire city.
These water dispensers give you about two liters of drinking water for only 1 baht ($0.03). The water in these machines is purified through reverse osmosis and is considered to be generally safe.
The one thing you may have to worry about is the machines’ filters not getting replaced often enough. I, nor any of the people I know using these machines have gotten sick from the water. You’re unlikely to have problems in the short or medium-term.
If you intend to live in Chiang Mai long-term, however, you’d probably be wise to invest in a personal water filtration system and replace the filters yourself every now and then. That would be the smartest solution for ideal health.
Generally speaking, however, the drinking water from these machines is convenient, cheap, and safe enough to not be overly concerned unless you’ve already optimized your diet in every other way (priorities!).