Every part of human society depends on clean water. We need to drink it to survive, we need to use it to water crops, and we even need to use it for most manufacturing processes. Industrial water use is not the biggest consumer of water, but it is a large one, and anyone who wants to understand the importance of clean water to the world needs to understand how its industrial role.
The most familiar use of water in an industrial setting is cleaning. Most modern factories require extreme precision to create their products, and an excess of dirt or grit can easily lead to errors. Machines that rely on many moving parts can also jam and break down if they are not cleaned regularly, and any product that is intended for human consumption needs to be made on clean machines for hygienic reasons.
It is also vital that the water be clean. If the water is impure, it can spread more contaminants on the devices. In some cases, that is only a minor problem. In others, such as in the chemical or food industries, that contamination could destroy the entire product.
Factories and power plants tend to get very hot. In many cases, cooling the factory with traditional air conditioning is prohibitively expensive. Those factories turn to other technologies to stay cool, most often by using a cooling tower. These towers rely on water to get rid of heat. Water falls down the inner walls of the tower while hot air rises through it. The air loses some heat when it makes contact with the water, which evaporates and forms a warm mist that can leave the tower. Excess water is collected, pumped back to the top of the tower, and reused.
Power is vital for modern industry, and a great deal of it comes from water. Many factories rely on hydroelectric power to function, but some also use running water directly to power machines. This water needs to be fairly clean in order to make sure that it does not provide a friendly environment for bacteria, which can corrode most machines.
Water is one of the most important chemicals in the world. Many chemical reactions use it at some point, either as a source of hydrogen and oxygen, or to provide an environment that makes the reaction go properly. Most of the water that gets used for chemical reactions needs to be completely pure, even more so than drinking water. If the water contains any contaminants, even ones that are harmless to humans, those contaminants will serve as addiction reagents in the reaction. Depending on the situation, that might mean that the factory needs to filter the end product before use, or it could lead to a completely different set of reactions happening.