The line segment graph above represents the volume of water in the storage tank on a domestic property. The measurement is in the 100's of litres. To determine the number of litres of water used in the first 5 weeks of summer, we look at the graph and find the corresponding value on the y-axis. The value is 1800, which represents 1800 litres of water. Therefore, the answer is 1800, 1800 litres, or 1800l.