As a general rule the tap water in Mauritius is safe to drink, but always take care immediately after a cyclone or cyclonic storm as mains water supplies can become contaminated by dead animals and other debris washed into the system. Never drink from streams as this might put you at risk of waterborne diseases.
It's not safe to drink the tap water in Rodrigues; stick with bottled water if you visit the island.
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 64.04 / 100 (100 being best).
Numbeo considers this score to be "High"
1 adult could save about 562$ per year in Mauritius 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.