Two obvious main answers:

To help out during periods of drought and water shortage.

To save some money!

So, how much water do I use normally?  This depends a bit on the size of your household and a lot on your lifestyle and needs. From the numbers provide by Anglian Water this can range (typically) from 93 to 202 litres per person per day. If the “average” person is somewhere in the middle of their various groups I estimate the amount to be around 116 litres per person per day. This is quite a lot of water!

How can this average person be using this amount of water?  Again, it will vary a lot from person to person but below is my estimate of how they could be doing it. The main assumptions are that they spend most of the day at home and don’t have a swimming pool, run a business using a lot of water, have special medical needs, etc.

                      Thing                           Frequency      Litres Per Thing    Times     Total Litres Per Day 

Cup of tea/coffee/water         Daily                       0.25                    8                     2.0

Flush the loo                             Daily                        7.0                     8                    56.0

Wash & clean teeth                  Daily                        4.0                     2                    10.0

Washing up                               Daily                        5.0                     1                      5.0

Cooking                                     Daily                        3.0                     2                      6.0

Bath/shower                             Weekly                   58.0                   3                     25.0

Washing machine                    Weekly                   50.0                   1                       7.0

Wash car                                   Yearly                     60.0                   3                       0.5

Water garden                            Yearly                     30.0                 20                      1.5

Have visitors                             Yearly                   125.0                  6                       2.0

Odds and Ends                         Yearly                    15.0                  25                      1.0

                                                                                                                   Total   =     116 

This may be very different for some people but is a starting point for reference and comparison. 

One of the main issues that can be seen is the loo flushing which accounts for 48% of the average person’s water usage!!