1. U.S. Geological Survey (2019a) How much water is there on earth? https://www.usgs.gov/special-topics/water-science-school/science/how-much-water-there-earth. Latest access 22 Jan 2022
2. U.S. Geological Survey (2018) Where is earth's water? https://www.usgs.gov/special-topics/water-science-school/science/where-earths-water. Latest access 22 Jan 2022
3. U.S. Geological Survey (2019b) The fundamentals of the water cycle. https://www.usgs.gov/special-topics/water-science-school/science/fundamentals-water-cycle. Latest access 22 Jan 2022
4. Metcalf & Eddy, AECOM (2014) Wastewater engineering treatment and resource recovery, 5th edn. McGraw Hill Education, New York
5. US Environmental Protection Agency (1994) A plain English guide to the EPA Part 503 biosolids rule. https://www.epa.gov/sites/default/files/2018-12/documents/plain-english-guide-part503-biosolids-rule.pdf. EPA 832-R-93-003. Latest access 22 Jan 2022