In industrial processing water is used in numerous applications requiring likewise different qualities of water. Examples of different use are cooling water, water for rinsing and chemical production, boiler feed water, purified water, water for injection, just to mention a few of those.

A conventional surface water treatment plant consists of a multi-step process applying screen-filtration, coagulation and flocculation, sedimentation, sand filtration, and usually disinfection as a last step. Each step of this process has to be controlled to get an optimal performance of the overall process, which results in a complex control system.

Purification process refers to the removal of dissolved solids from feed water and process streams. Demineralization is a type of water purification. Demineralized water is usually made by using ion exchange, electrodeionization, or membrane filtration technologies, which can be more efficient for creating ultrapure water than processes such as distillation (where water is boiled in a still and condensed, leaving dissolved contaminants behind).