Could be the supply, but just as likely the entire building's water supply system is unmaintained and contaminated? Mold/mildew here grows in seconds.

Many people install multi-stage filtration systems, usually under the sink in the kitchen for home use. These cost a few baht per day, can be installed quite easily, have user-replaceable filters which can be ordered online. Your friend can go to HomePro for a selection. Simple really.

I haven't noticed any tap-water odors in years, but again, highly-dependent on location.