Houses could be designed to be 'autonomous', in that they are able to provide their own services, such as water, heating, cooling, sewage, and electricity, from natural sources without the need for fossil fuels and sewage treatment plants. This chapter suggests that sustainable design is impossible without a basic understanding and use of numbers. Autonomous systems have the potential to reduce environmental impacts in other fields, one of which is transport. The design of autonomous, sustainable buildings is not solely a technical matter, it is also a matter of making choices about lifestyle and values. The choices made in appliance use have a significant effect on the design of autonomously serviced buildings. The energy needed for water heating will depend on the amount of water needed by the household. Waterless toilets are available which make the sewage into a garden fertiliser, but the most effective models are bulky, and need to be designed into a building.