Water and energy management are important and interrelated issues. Sewage treatment, that is, the physical, chemical and biological processes used to clean industrial and domestic wastewater, has improved significantly over the past 20 years, with approximately 75% of UK rivers now of good biological and chemical quality. However, the energy required to treat sewage to this standard is high; the water industry is the fourth most energy intensive sector in the UK. Further tightening of water quality standards suggest energy costs will increase. This POSTnote evaluates options for sewage treatment in terms of energy conservation and renewable energy generation.