noun
water offered to the gods and Buddha
A religious offering of water placed on a Buddhist altar or Shinto kamidana. The term is specific to ritual contexts.
毎朝、仏壇に御供水を供えます。
Every morning, I offer water to the Buddhist altar.
神棚の御供水は毎日取り替える。
The water offered at the Shinto altar is changed daily.
A broader term for offerings (food, drink, etc.) to deities or Buddha; 御供水 is specifically water.
Compound of 御 (honorific prefix) + 供 (offering) + 水 (water). The reading ごくうすい reflects the honorific 御 (ご) and the on'yomi of 供水.