The maximum density of water in its liquid form occurs at around 4°C (under normal pressure p = 1013,25 hPa). If the pressure is increased (or decreased) would the point of maximum density still be at the exact same temperature?
As usual, the answer to such questions is on Martin Chaplin's water anomalies site:
"Increased pressure reduces the temperature of maximum density." http://www1.lsbu.ac.uk/water/density_anomalies.html#Pdens