I found the United Utilities Education Interactive which explains how our water is collected and what happens to it when it goes down our drains.
They both watched the videos very intently and when it had finished Louby proclaimed, wow that is very amazing... (amazing being her favourite word at the minute) I asked them if they had any questions and they just said can we watch TV now...and off they toddled.....
I love that part of our education journey, they can take in what they need and off they go processing the information and out it will pop in a few weeks or months.
I will look for some ideas on expanding our Water education and find some interesting experiments using water that we can play with and a visit to a water treatment plant will be on the cards in a few years when they are a bit older.
The Education Interactive site is great and also caters for older kids so a great one to look at and get some ideas from.