According to the WHO, tap water is safe for consumption for 57% of the country.
There is a divide between rural and urban areas, tap water is safe to drink in 67% of urban areas, while it's only safe to drink in 46% of rural areas.
While many Guatemalans drink the tap water (often through necessity rather than choice), it is not recommended that foreigners do so.
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 40.48 / 100 (100 being best).
Numbeo considers this score to be "Moderate"
1 adult could save about 730$ per year in Guatemala 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.