How do you find the water pressure at the bottom of the 55-m-high water tower?

-- What's the volume of a cylinder with radius=1m and height=55m ?

         ( Volume of a cylinder = π R² h )

-- How much does that volume of water weigh ?

            1 liter of water = 1 kilogram of mass
            Weight = (mass) x (acceleration of gravity) 

-- What's the area of the bottom of that 1m-radius cylinder ?

       Pressure  =  (force) / (area)