One possibility is the word pipe. For example, water flows threw pipes.
flume
Wash is a four letter word meaning "to clean with water".
Wash is a four letter word meaning "to clean with water".
chute
crate, write, chute
A "bay" is a small protected body of water that is a four-letter word.
scum
best
'chute
Flow or tide
aqua, agua
tide