Is tap water really that cheap? Where I am from tap water isn't safe to drink to we have to buy big jugs (5 gallons) of purified water.
Online it says that one glass of water is between 200ml and 250ml. Let's be conservative and say 200ml per glass.
200ml x 8 glasses x 365 days = 584,000ml/year = 154.28 gallons per year
Rounding up to 155 gallons, you would need 31 5-gallon water jugs a year. In my area, a jug costs you about $1USD (give or take, depending on the exchange rate) so it would cost you $31USD per year to fulfill your water drinking needs. It is difficult for me to imagine that tap water is actually 100 times cheaper than that...
Just looked it up, tap water does indeed cost $0.01USD per 5-gallons in the US.