Traditionally it's not a "mass" of water, it's a pound (unqualified) of water. There's an issue right there and one that cracks the door open to "how is pound

Traditionally it's not a "mass" of water, it's a pound (unqualified) of water. There's an issue right there and one that cracks the door open to "how is pound of water created". Leading into (depending on path to above) the issue of density of water, while famously and often described as incompressible, water reaches max density at 4 C, 3.99 degrees (Kelvin or Celsius) above water's triple point.