Water's always easier in metric. Your radius is 4.5ft*30.5cm/ft, or 137.25cm. Your depth is 26in*2.54cm/in, or 66cm. Your volume is pi * 137.25^2 * 66, or about 3.9 million cc, so at 1g/cc the water would weigh about 3.9 metric tons, or 4.3 Imperial tons.

Peter