In restaurants, choose tap water and don't feel like a cheapskate. I usually do. Ask for a lemon or lime for added flavour. If you like sparkling water, order and pay the price. I sometimes do.
Tap water is best for the environment.
Millions of tons of plastic are used to bottle water every year, you are adding to the heap. When plastic bottles are manufactured, toxic chemicals and gases are released into the environment. You are adding to this. Europeans prefer the taste of bottled water. It tastes better than their tap water.