According to the WHO, tap water is safe for consumption for 100% of the country.
Tap water is almost always fine to drink, though restaurants will sometimes deny this as an excuse for insisting on serving mineral water.
According to the CDC tap water is generally safe for consumption.
According to the Numbeo water drinkability and accessibility index, tap water has a score of 68.86 / 100 (100 being best).
Numbeo considers this score to be "High"
Belgium is a member of the European Union which ensures tap water safety across its countries.
1 adult could save about 701$ per year in Belgium 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.