noun
water supply inlet/outlet (firefighting)
Technical term used in fire protection; refers to the connection point on standpipes or dry risers where firefighters supply water.
消防隊が送水口にホースを接続した。
The fire brigade connected a hose to the water supply inlet.
この建物の送水口は1階の外壁にある。
The water supply inlet for this building is on the exterior wall of the first floor.
連結送水管 refers to the entire combined standpipe system, whereas 送水口 is the connection point on that system.
Compound of 送水 (water supply) + 口 (opening/mouth). The exact historical derivation is uncertain, but the term is a straightforward technical compound.