any given material. In the absence of a comprehensive global embodied energy public dynamic database, embodied energy calculations may omit important data on, for example, the rural road/highway construction and maintenance needed to move a product, marketing, advertising, catering services, non-human services and the like. Such omissions can be a source of significant methodological error in embodied energy estimations. Without an estimation and declaration of the embodied energy error, it is difficult to calibrate the sustainability index, and so the value of any given material, process or service to environmental and economic processes. Standards The SBTool, UK Code for Sustainable Homes was, and USA LEED still is, a method in which the embodied energy of a product or material is rated, along with other factors, to assess a building's environmental impact. Embodied energy is a concept for which scientists have not yet agreed absolute universal values because there are many variables to take into account, but most agree that products can be compared to each other to see which has more and which has less embodied energy. Comparative lists (for an example, see the University of Bath Embodied Energy & Carbon Material Inventory) contain average absolute values, and explain the factors which have been taken into account when compiling the lists. Typical embodied energy units used are MJ/kg (megajoules of energy needed to make a kilogram of product), t (tonnes of carbon dioxide created by the energy needed to make a kilogram of product). Converting MJ to t is not straightforward because different types of energy (oil, wind, solar, nuclear and so on) emit different amounts of carbon dioxide, so the actual amount of carbon dioxide emitted when a product is made will be dependent on the type of energy used in the manufacturing process. For example, the Australian Government gives a global average of 0.098 t = 1 GJ. This is the same as 1 MJ = 0.098 kg = 98 g or 1 kg = 10.204 MJ. Related methodologies In the 2000s drought conditions in Australia have generated interest in the application of embodied energy analysis methods to water. This has led to use of the concept of embodied water. Data A range of databases exist for quantifying the embodied energy of goods and services, including materials and products. These are based on a range of different data sources, with variations in geographic and temporal relevance and system