reservoir

A natural or artificial pond or lake used for the storage and regulation of water.

A receptacle or chamber for storing a fluid.

An underground accumulation of petroleum or natural gas.

A large or extra supply; a reserve.

An organism or population that directly or indirectly transmits a pathogen while being virtually immune to its effects.

To furnish with a reservoir; also, to collect and store in a reservoir.

In organ-building, same as storage-bellows. See bellows, 3, and organ, 6.

A place where anything is kept in store: usually applied to a large receptacle for fluids or liquids, as gases or oils.

Specifically A place where water collects naturally or is stored for use when wanted, as to supply a fountain, a canal, or a city, or for any other purpose.