The water safety report based on quality measurements for Pisa can be found here.
Search for โPisaโ and select the water source
According to the Numbeo water drinkability and accessibility index, tap water has a score of 62 / 100 (100 being best).
Numbeo considers this score to be "High"
1 adult could save about 314$ per year in Pisa 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.