Study the graph below, which shows the UK's average daily per capita domestic water consumption between 2005 and 2025.

Identify the decrease in average daily per capita domestic water consumption in the UK from 2005 to 2025.
21 litres21\text{ litres}21 litres
20 litres20\text{ litres}20 litres
28 litres28\text{ litres}28 litres
38 litres38\text{ litres}38 litres