The metric system is pretty good at that: 1 ml H2O = 1 cm^3 = 1 g, and 1 calorie will increase its temperature 1 deg C (assuming 1 atmosphere pressure, and a certain water temperature).
Anyone have a rhyme for it?
Sounds great, until you add pretty much anything to the water.
Same with pints and pounds.
My favorite part about the metric system is that the weight of 1 kilo is the same as 1 liter of H2O. This was extremely useful for me in a past life.
You hit! From my experience, metric system is best for pharmaceutical calculations, like "how many water need to got 40% alcohol", and it's also extremely important for taste, as in many cases better 38%.