How much you save when you replace your old toilets with low flush toilets ?

I have one of my client,  for whom we were planning to buy old house and renovate it as much as possible and make it energy efficient. We were making list  which things to replace in order to make a home energy efficient  ? 
One of the thing we don't pay attention is toilets. 
Do you know how much water do we flush each time ? 

Check out the table below, and if you would like to change your toilet and if you are living in Greater Toronto Area, refer links below you may save when you buy energy efficient toilets.


Resident of Brampton, Mississauga or Caledon

For Resident of Vaughan, Richmond Hill, Markham, Stoughville

For Resident of City of Guelph