paper is recommended. However, septic tanks remain popular because they permit standard plumbing fixtures, and require few or no lifestyle sacrifices. Composting or packaging toilets make it economical and sanitary to throw away sewage as part of the normal garbage collection service. They also reduce water use by half, and eliminate the difficulty and expense of septic tanks. However, they require the local landfill to use sanitary practices. Incinerator systems are quite practical. The ashes are biologically safe, and less than 1/10 the volume of the original waste, but like all incinerator waste, are usually classified as hazardous waste. Traditional methods of sewage handling include pit toilets, latrines, and outhouses. These can be safe, inexpensive and practical. They are still used in many regions. Storm drains Drainage systems are a crucial compromise between human habitability and a secure, sustainable watershed. Paved areas and lawns or turf do not allow much precipitation to filter through the ground to recharge aquifers. They can cause flooding and damage in neighbourhoods, as the water flows over the surface towards a low point. Typically, elaborate, capital-intensive storm sewer networks are engineered to deal with stormwater. In some cities, such as the Victorian era London sewers or much of the old City of Toronto, the storm water system is combined with the sanitary sewer system. In the event of heavy precipitation, the load on the sewage treatment plant at the end of the pipe becomes too great to handle and raw sewage is dumped into holding tanks, and sometimes into surface water. Autonomous buildings can address precipitation in a number of ways: If a water-absorbing swale for each yard is combined with permeable concrete streets, storm drains can be omitted from the neighbourhood. This can save more than $800 per house (1970s) by eliminating storm drains. One way to use the savings is to purchase larger lots, which permits more amenities at the same cost. Permeable concrete is an established product in warm climates, and in development for freezing climates. In freezing climates, the elimination of storm drains can often still pay for enough land to construct swales (shallow water collecting ditches) or water impeding berms instead. This plan provides more land for homeowners and can offer more interesting topography for landscaping. A green roof captures precipitation and uses the water to grow plants. It can be built into a new building or used to replace