gallons
It depends on how big your bathtub is.
75 gallons. Typical bathtub dimensions 5ft x 2 ft x 1 ft (waterline) = 10 cubic ft = ~75 gallons or 284 liters
They vary in size, but I have one that is a little larger than the average size and it holds around 75 gallons of water.
30 gallons
It depends on how big your bathtub is.
Because we take the water's space so it needs to rise. It was discovered by Aristotle when he fulled his bath full of water and it overflowed.
Assuming that you are asking does a bathtub hold 350 ml of water: 350 ml of water is not very much water, a typical water bottle that you hold in your hand has more than 350 ml of water in it, so a bathtub big enough to hold a person will hold many times that much.
over 45,000 gallons per year
Depends on the tub, but usually about 40-50 gallons.
20ml
Er...55 gallons?
Clayey soil hold the most water of all, as sand and chalk. Loamy soil holds water but not as much as clayey.