Harry, I'm going to be pedantic - sorry.
Water colour is different depending on where you are. EG the "blue" Danube is indeed bluer than the muddy Thames. And also depending on season & time of day.
BTW this is worse with ocean colours. The Atlantic is a grey-green but where I live, the Pacific is often a shade of blue that looks almost ridiculously fake.
https://www.queensland.com/gb/en/places ... queenslandSo, the bottom line is almost any blue, green, grey, brown will be accurate for some body of water, somewhere.
If you want a specific body of water, google it & match the colour against a Vallejo colour chart.
cheers, donald