Tap water is not safe to drink. Use bottled or filtered water; for the former, look for the small round โSLSIโ logo, which shows the water has been tested by the governmentโs Sri Lanka Standards Institution (the majority of local brands).
According to the CDC tap water is generally not safe for consumption.
According to the Numbeo water drinkability and accessibility index, tap water has a score of 63.69 / 100 (100 being best).
Numbeo considers this score to be "High"
1 adult could save about 358$ per year in Sri Lanka by drinking tap water instead of buying bottled water.
๐ณ Drinking tap water would also help with reducing your plastic footprint and improve environmental pollution.