According to the WHO, tap water is safe for consumption for 43% of the country.
Tap water in Mexico is mostly not safe to drink. Purified water in plastic bottles is sold everywhere and is also available from large dispensers in some accommodations. The most effective means of water purification is vigorous boiling for one minute (three minutes at altitudes over 2000m). Another option is a SteriPen (www.steripen.com), which kills 99.9% of bacteria and viruses with ultraviolet light. Pregnant women and those with a history of thyroid disease should not drink iodinated 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 54.18 / 100 (100 being best).
Numbeo considers this score to be "Moderate"
1 adult could save about 438$ per year in Mexico 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.