I think that's backwards -- if it's a very accurate simulation of water, it will pass the U test, but you can add hacks to make a simple, inaccurate system pass

I think that's backwards -- if it's a very accurate simulation of water, it will pass the U test, but you can add hacks to make a simple, inaccurate system pass it, too. See, for example, Dwarf Fortress's pressure system: http://dwarffortresswiki.org/index.php/DF2012:Flow#Fluids_under_pressure.2C_aka_Teleportation http://dwarffortresswiki.org/index.php/DF2012:Flow#Fluids_un....