You can measure the savings the easy way by seeing
the effect on your utility bills however be cautious since savings
can be masked by other events occurring at the same time e.g.
an extra person in the house increases water use. Water bill can be infrequent meaning it can be a long time before you find out if you are really saving water. Also water
use is not constant with for example large peaks at weekends and
higher use at certain times of the year.
If you do use the water bill as a guide beware of estimated readings. They are usually wrong and often in the water companies favour. Whenever an estimated bill arrives phone through the correct reading and get a new bill, this helps with keeping control of costs.
The best way is to keep a record of the water
meter reading every few weeks, trying to keep as regular as
possible, calculating the savings of water used and cost
each time. From experience checking around every four weeks
works best. To make this simpler and remove the need for manual calculations you can use EnCalcLU an electricity use calculator which is free for non commercial use. Doing this also enables things going wrong to be spotted early and hence saving unnecessary cost.
As part of monitoring and maintaining savings it is a good idea to get into the habit of going round the house each night to make sure all the taps are turned off.
You can also use the water meter readings to check for leaks. The meter reading should not be increasing with everything turned off. I usually wait around half an hour after being sure everything is off before watching the meter for around a minute to make sure the reading is steady. Any movement of the reading indicates a possible leak, either from for example a dripping tap or cistern or more seriously a leak from a pipe.