depends how big.
sometimes mL, sometimes L, and if it gets that big, Tons.
Litres for a domestic aquarium, kilolitres for a large [public] aquarium.
Liquid measure is always called Fluid Measure. Quantity or Volume of fluid is never measured in Centimetres. Volume of fluids is measured in Litres or Millilitres. If, and only if, the fluid is pure water, then the number of ml of it will be the same as the number of cubic centimetres (cc) of it.
Square metres.
Since water towers generally have a very large capacity, I would say that cubic meters might be the best bet. You can measure the total volumetric capacity of the water tower in cubic meters and then determine the volume of water that is currently in the water tower. However, an amount of water can also be measured in liters.
There is no set measurement for this, because it varies from person to person. If you wish to measure it with existing metric units, however, the best option would be centimeters because a meter is much too large, while it is very difficult to come across something that measures in decimeters.
it is used to measure large amount of substances
A large plastic bottle is 2 liters.
Gallons (standard) or liters (metric).
Litres for a domestic aquarium, kilolitres for a large [public] aquarium.
Well that would depend on the size of the plastic bottle. If the bottle is large use litters or "L" for short. If the bottle is small use milliliters or "ml" for short.
meters or kilometers.
Liquid measure is always called Fluid Measure. Quantity or Volume of fluid is never measured in Centimetres. Volume of fluids is measured in Litres or Millilitres. If, and only if, the fluid is pure water, then the number of ml of it will be the same as the number of cubic centimetres (cc) of it.
Square metres.
Kilogram
The kilogramme.
Cups
Litres for small quantities, and cubic km for large ones such as the oceans.