I reckon that water under high pressure does have a somewhat higher density. However water is pretty much the textbook example of an incompressible fluid so the

I reckon that water under high pressure does have a somewhat higher density. However water is pretty much the textbook example of an incompressible fluid so the difference will probably be rather small. Edit: Found a direct quote on wikipedia https://en.wikipedia.org/wiki/Properties_of_water#Compressibility https://en.wikipedia.org/wiki/Properties_of_water#Compressib...: >The low compressibility of water means that even in the deep oceans at 4 km depth, where pressures are 40 MPa, there is only a 1.8% decrease in volume.[40]