The Earth’s water resources are found in a variety of settings. The majority of water is saline, while only a small fraction is freshwater. Some freshwater is easier for humans to access for their use, while other freshwater is confined in sources that are difficult to access. Humans need a minimum of 7.5–15 liters (L) of water per day for basic survival, but need much more water for activities related to long-term hygiene, agriculture, industry, and business. Water supply and demand are calculated for populations by assessing the quality and quantity of water available, how to store and transport it, what uses it is desired for, and how its use affects the environment. The World Health Organization (WHO) defines a safely managed water supply as meeting standards related to water quality, quantity, and the timing of its availability. Since the launch of the Sustainable Development Goals (SDG), including SDG6 focused on water and sanitation, the World Health Organization/United Nations International Children’s Emergency Fund (WHO/UNICEF) Joint Monitoring Programme for Water Supply, Sanitation, and Hygiene has assessed the availability of safely managed water to measure progress toward the goal. Progress has been made toward increasing access to safely managed drinking water in the twenty-first century, but there were still two billion people lacking access in 2020. Climate change has affected the supply and demand for safely managed water by changing temperature and rainfall patterns worldwide, contributing to water scarcity in populated areas and intensifying weather events such as flooding and drought.