low water vs low tide

low water and low tide both are nouns.

Word	Noun	Adjective	Verb	Adverb
low water	Yes	No	No	No
low tide	Yes	No	No	No

As nouns, low water and low tide are synonyms defined as:

low water (noun)	low tide (noun)
the lowest (farthest) ebb of the tide	the lowest (farthest) ebb of the tide