Raw water is water found in the environment that has not been treated and does not have any of its minerals, ions, particles, bacteria, or parasites removed. Raw water includes rainwater, ground water, water from infiltration wells, and water from bodies like lakes and rivers.

Raw water is generally unsafe for human consumption due to the presence of contaminants. A major health problem in some developing countries is use of raw water for drinking and cooking.

Without treatment, raw water can be used for irrigation, construction, or cleaning purposes. Farmers use it to water their crops and give it to livestock to drink, and it can be stored in man-made lakes or reservoirs for long periods of time. Construction industries can use raw water for making cement or for damping down unsealed roads to prevent dust rising. Raw water can also be used for flushing toilets and washing cars, as well as any other purposes that do not require it to be consumed by humans. Water in this form is considered raw, as opposed to water which has been treated before consumption, such as drinking water or water which has been used in an industrial process, such as waste water.

Raw water flushing is a method of water conservation where raw water is used for flush toilets.

The composition of raw water is naturally variable, but commonly contains one or more of the following significant contaminants, in the form of dissolved ions, particles and living organisms:

Other, less common, contaminants of raw water include:

These contaminants can be harmful to humans if they drink raw water containing them, or if the water is not treated properly before consumption. The contaminants can also have an effect on the local ecosystem. For example, endocrine disrupting chemicals can have harmful effects on fish populations living in natural lakes and rivers. These growing health concerns have led to the development of guidelines, such HACCP (Hazard Analysis and Critical Control Points), for the production of safe drinking water from wastewater and raw water, and research into sustainable water supply alternatives.

Raw water can be used for many purposes, such as cooling water, water for rinsing and chemical production, purified water, and drinking water. However, due to the possible contaminants, raw water must be treated before it is allowed for human consumption or industrial use. There are several steps involved in the treatment of raw water, and different methods in which it can take place.