Our modern sewage system relies on vast amounts of water and this causes huge problems. Perhaps the greatest being that the anaerobic microbes that break down human waste in water are inefficient, produce greenhouse gases, and then waste ends up in the rivers and seas producing algal blooms and foul smells. Whereas their descendants on land (aerobic microbes) are extremely efficient and only produce CO2, H2O and organic matter. So what went wrong? I will describe the history of the modern sewage system and how it broke the natural nutrient cycle, causing pollution, health problems and costing a lot of public money, and then conclude with the maths, chemistry and biology of a micro self-sustaining aerobic sewage system on a houseboat.