Lee I read through your boards, and my concern is this - you will need to grow a large number of plants at a very quick rate in order to allow the children to pick leaves every time they wash their hands. If you have a school with 50 children, and they each wash their hands three times a day, they could be picking 150 leaves a day. Do you know how quickly these plants grow? Do you know how many children are in the average village school?
If the grey water has sand mixed into it from the exfoliating process, will the sand dropping on the plants affect the plants in any negative ways?