Short answers, pulled from the story.
Drinking water, or potable water, is water safe for ingestion either drunk directly or taken in through food preparation. The amount needed to maintain good health varies with physical activity, age, health issues, and environment, and people working in a hot climate may require up to 16 liters a day.
As many as two billion people lack safe drinking water, and developing countries are most affected. Contaminated water is estimated to cause more than half a million deaths per year, and an estimated 1.8 billion people use a source that may be contaminated by feces.
Drinking water commonly comes from springs, hyporheic zones and aquifers, rainwater harvesting, surface water from rivers, streams and glaciers, or desalinated seawater. An experimental source is solar-powered atmospheric water generators, and springs are often used for bottled waters.
Drinking water quality parameters fall into three categories: microbiological, chemical and physical. Microbiological parameters include coliform bacteria, E. coli, Vibrio cholerae, Cryptosporidium, Giardia lamblia and Legionella, while chemical parameters include heavy metals, nitrates, arsenic, pesticides and PFAS.
Notable incidents include the 1854 cholera outbreak traced to London's Broad Street pump, arsenic poisoning of groundwater in Bangladesh recognized in 1993, the 2000 E. coli outbreak in Walkerton, Ontario that killed seven people, and the Flint, Michigan crisis that started in 2014.
Most water requires treatment such as boiling, filtration, chemical disinfection, or exposure to ultraviolet radiation, with chlorination being the most widely used method. Christchurch, New Zealand is one of few large urban areas with water pure enough to need no treatment of the raw water.
According to a report by UNICEF and UNESCO, Finland has the best drinking water quality in the world. The World Health Organization considers access to safe drinking water a basic human right.