Tap water is deemed unsafe to drink throughout Laos. Although the quality of water varies, some coming piped, some from a well, one should always assume it is unsafe to drink without boiling.
Tap water in Laos isn't purified properly at a treatment plant and underground pipes are generally dirty. The consumption of unsafe drinking water can cause major diseases, such as diarrhea, cholera, dysentery and typhoid fever.
You can shower and brush your teeth with the local water, but your drinking water should be bottled water or boiled water. A large range of bottled water is very inexpensive and they are available at many places.
The old claim that salad items should be avoided in Laos, because vegetables were washed in tap water is no longer true. Fruit and vegetables can be enjoyed freely in Laos. Many foreigners cook at home, washing vegetables in tap water with no ill effects. Ice in drinks is generally okay, but you may want to decline ice in non-tourist areas.
If you are staying in a hotel or guest house, they will supply bottled water free of charge each day you are there. If you are invited to a Lao home, you may notice that they have filtered and purified water in large containers. This water is perfectly safe to drink.
Since the weather in Laos will be extremely hot and humid especially in March and April, pay attention to your body, carry a bottle of water or liquid drink with you, and continually hydrate yourself.