We recommend drinking bottled water when you’re in Koh Samui.
Much of the tap water on the island is not safe to drink. It doesn’t taste great, either, so we don’t recommend drinking water straight from the tap in Koh Samui or even using it to clean your teeth.
Safe, bottled mineral water is available all over the island so it’s easy to stock up while you’re there on vacation. You should expect to pay around $2 (68 baht) for a 2-litre bottle of mineral water from a local supermarket.
If you do decide to drink the tap water in Koh Samui, we recommend that you boil it first or use water purification tablets.