Tap water in Cuba is not reliably safe to drink and outbreaks of cholera have been recorded in the past few years. Bottled water called Ciego Montero rarely costs more than CUC$1, but is sometimes not available in small towns. Stock up in the cities when going on long bus or car journeys.
According to the CDC tap water is generally not safe for consumption.
According to the Numbeo water drinkability and accessibility index, tap water has a score of 48.61 / 100 (100 being best).
Numbeo considers this score to be "Moderate"
1 adult could save about 686$ per year in Cuba 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.