The phrase "no good" typically refers to quality or condition.
The phrase "not good" can refer to quality, condition, or something that one finds to be bad or not pleasing, or a person
It �s raining, so we can �t go to the park. That �s not good. - This is something the speaker and the listener find to be unpleasing or bad.
This keyboard doesn �t work anymore. Throw it away. It �s no good. Here, the speaker is referring to the condition of a keyboard. (You could say "not good" here, but this is an example of how someone would typically use "no good.)
no good can also be used just as informal language.
I "stole" this answer from a forum called english-test :p so it �s not my own lol but I thought it would be helpful :) thanks to the person who submitted it to that forum :)
So since in your sentence its a quality and condition of the water. no good would be correct :)
Hugs
Sara
