Boiled water is the only water used in the process of tea making. The Russian language actually makes a clear distinction between "boiled water" and "raw water". The latter is often misinterpreted by non-native speakers as wet water (as opposed to dry water?), which is funny.

Я НИКОГДА не задумывался, что со словосочетанием "сырая вода" что-то не так. Мне в принципе не приходило в голову об этом задуматься.