Is tap water safe to drink in Shanghai?

Best not to. The water leaves the treatment plant to standard, but it can pick up impurities from aging building plumbing and rooftop tanks on the way to your tap. Almost no one in Shanghai drinks unboiled tap water, and as a visitor with an unaccustomed stomach, you shouldn't be the exception.

Completely fine. Brushing your teeth, rinsing fruit, and showering with tap water carry negligible risk. You don't need bottled water for any of that.

The local default is boiled water. Nearly every hotel room and apartment has an electric kettle, and hot-water dispensers are common in public spaces. Boiling makes tap water safe to drink, and hot water is itself the cultural default — don't be surprised to be offered a cup of plain hot water at a restaurant.

Bottled water is inexpensive and sold in every convenience store, vending machine, and supermarket — pay by scanning Alipay or WeChat Pay. A large bottle costs a few RMB. It's the simplest option if you'd rather not bother boiling.