Formal:
* शौचालय (shauchalaya): This is the most formal and general term for a restroom.
* पानीघर (paani ghar): This literally translates to "water house" and is sometimes used for a restroom, especially in older buildings.
Informal:
* टॉयलेट (toilet): This is the most common and informal word for a restroom, borrowed from English.
* बाथरूम (bathroom): This term is also common and often used for a room with a toilet, sink, and sometimes a shower or bathtub.
For asking where the restroom is:
* शौचालय कहाँ है? (shauchalaya kahaan hai?) - Where is the restroom?
* टॉयलेट कहाँ है? (toilet kahaan hai?) - Where is the toilet?
* बाथरूम कहाँ है? (bathroom kahaan hai?) - Where is the bathroom?
It's best to use the more formal terms "शौचालय" or "पानीघर" in formal settings like offices or schools. In casual settings, "टॉयलेट" or "बाथरूम" are perfectly acceptable.