In Bhutan, drinking tap water is not recommended unless it has been boiled or chemically cleansed. Hotels, small and large retail establishments, and restaurants all have access to bottled mineral water. Foreign visitors will receive bottled water from their tour operator or guide. Since your tour fee includes everything, you are welcome to take as many of the bottles they have in the car as you like.
If free bottled water is not offered in the hotel rooms, an electric kettle for boiling water ought to be available. You can always request some boiled water from your hotel if it doesn't appear to be as clean and good as you would have liked. When trekking in Bhutan's remote regions, it is also a good idea to have water-purifying tablets. However, the majority of hotels offer either mineral or heated water for guests to drink. Since drinking tap water is unsafe, using mineral or heated water to brush your teeth is also safe (after cooling). Since salads are likely to have been washed with tap water, it is advised for tourists to avoid eating them at mealtimes. Be sure to inspect the seal when purchasing bottled water if you plan to drink it. Avoid ice as much as you can because it can have been made with regular tap water. Additionally, stay away from fresh fruit juices because they can have been diluted.