水净化（英语：Water purification），是指从原水中除去污染物的净化过程，其目的是以特定的进程达到把水净化的效果，并用水作不同的用途；大多数的水都是提供人类饮用的。净化水亦可作很多其他不同的用途如医学、药理学、化学及工业之用。

大部分地区在进行水质消毒时，都会使用消毒剂(传统的氯气或氯胺)。在消毒的过程中，低含量的消毒副产物在消毒剂与水中的有机物相遇时而作出化学反应而产生。而消毒副产物有机会是一种致癌物质，水净化可以是去除消毒副产物和水中带的沙、有机质的悬浮微粒、寄生虫、篮氏贾第鞭毛虫、隐孢子虫、细菌、藻类、病毒及真菌等等，及矿物如钙、二氧化硅及镁等等，和一些有毒性的金属如铅、铜及铬等等。

Water purification is the process of removing undesirable chemicals, biological contaminants, suspended solids and gases from contaminated water. The goal is to produce water fit for a specific purpose. Most water is disinfected for human consumption (drinking water), but water purification may also be designed for a variety of other purposes, including fulfilling the requirements of medical, pharmacological, chemical and industrial applications. The methods used include physical processes such as filtration, sedimentation, and distillation; biological processes such as slow sand filters or biologically active carbon; chemical processes such as flocculation and chlorination and the use of electromagnetic radiation such as ultraviolet light.