Question

what is the unit used to measure Dam water

Answer 1

Water measurement units :
There are two conditions under which water is measured -- water at rest and water in motion.
Water at rest [like ponds, reservoir ] is measured in units of volume.

common units : cubic  foot

But the bigger units that are used to measure the volume of water in reservoirs or dams or river flow is Tmcft.

Tmcft ---- one Thousand million cubic feet .
1Tmcft = 2.831 x 10¹⁰ litres.

Answer 2

The water in the dams is considered as stored water or impounded water.

It can be measured either in terms of 'Cusecs' or as 'Tmcft'.

Cusec is the informal shorthand for "cubic feet per second". It can be converted to 28.317 litres per second.

Tmcft or TMC is the abbreviation for one thousand million cubic feet. It is equal to 2.83168466 x 10¹⁰ litres.