You mean stuff like: Water as ballast (instead of concrete) inside washing machines right?,(reply>), @BouncingCookie But for a country like Australia that is short of water, this concept would not be good. We go from droughts to flooding rains.,(reply>), It is probably cheaper to just drain the water after each use than putting in extra parts. Water in my country only costs around 2.17€ for 1000L with sewage fees. (This is also the  price for 3 bottles of water in the supermarket with the same qualitiy of water.),(reply>), we could stick some neutron star in there instead,(reply>), The concrete blocks can usually be unbolted.,(reply>), Heavy water would save space :)