Drinking tap water isn't recommended in Peru – or anywhere else in South America, but it’s generally considered safe to drink tap water that has been boiled or filtered. There's no need to worry about keeping your mouth closed while you shower, but if you have a particularly sensitive stomach, you may wish to use boiled or filtered water to brush your teeth or wash fruits and vegetables.
When ordering cocktails or smoothies, try to avoid drinks with ice. You can always ask the waiter or vendor if they use filtered water to make ice, but if you’d rather not risk it, just order your drinks 'sin heilo' (without ice).
Single-use water bottles contribute to a huge environmental problem, so your best bet is to bring a portable water filter or water purifying tablets and a large reusable bottle to refill at canteens or hotels. Your local leader will always point out where filtered water can be found.