A day at Grandma and Grandpa's

Today I went to Bristol to visit my Grandma and Grandpa. I read 'Swallows and Amazons' to Grandma. They told me about the Monastery at Fountains Abbey which was inhabited by Cistercian monks from 1132 AD. The monks had a very advanced waterworks system. They made beer using spring water from the nearby hills. When they went to the toilet the wooden lavatory bench was right over the river so all the dirty water was washed away downstream. This meant that the river was very dirty, smelly and polluted but downstream it soon became fairly clean and then further down became clean again. The plants and bacteria in the river cleaned the dirty water this is rather like what happens in a modern sewage works.