The municipal water supply in the capital and in the majority of major towns can be trusted. If youโre trekking, drink only from streams at a higher altitude than nearby villages. It's always a sensible precaution to boil, filter or chemically disinfect water.
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 46.74 / 100 (100 being best).
Numbeo considers this score to be "Moderate"
1 adult could save about 1606$ per year in Papua New Guinea 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.
Like in most countries, water quality and accessibility differs from location to location, therefore it's the best to check the information available on that place.