A cubic metre of pure water at the temperature of maximum density ( 3.98 Â C ) and standard atmospheric pressure ( 101.325 kPa ) has a mass of 1000 kg , or one tonne . A cubic metre of pure water at the temperature of maximum density ( 3.98 Â C ) and standard atmospheric pressure ( 101.325 kPa ) has a mass of 1,000 kg , or one tonne .