Describe selected developments in the field of improving the sustainability of medium density residential development projects in Australia. Select and describe some energy, water or waste systems which may be incorporated in current residential projects to assist their environmental performance. This can mean building products or processes. It will be necessary to define the concept of sustainability and list the benefits and disadvantages of each system described, both on the building occupants and on the environmental footprint of the building. Express an opinion (with references) about the likely cost to the construction industry and the consumer of including these options in residential development.