Water rate? (4)
I believe the answer is:
knot
This clue might be a double definition.
'water' is the first definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'rate?' is the second definition.
Can you help me to learn more?
(Other definitions for knot that I've seen before include "Small northern sandpiper" , "Small cluster - huddled group - sheepshank, for example" , "Tie (or what is put in one?)" , "Granny or reef, perhaps?" , "Fastening formed by tying string etc" .)