Water (H2O) is a fundamental compound found everywhere on Earth, from oceans to the atmosphere. It is indispensable for all known life forms, playing a central role in biological processes and environmental systems. Water’s diverse forms and classifications reflect its varied occurrences and applications, ranging from what we drink daily to its presence in vast natural landscapes.
Water for Drinking
Water intended for human consumption undergoes various treatments and classifications to ensure its safety and quality. Tap water, supplied through municipal systems, originates from sources like rivers, lakes, or groundwater and is treated at purification plants before distribution. The Environmental Protection Agency (EPA) sets standards for public drinking water.
Bottled water offers various options. The U.S. Food and Drug Administration (FDA) regulates it as a packaged food product, establishing standards for quality and processing, including hygienic conditions and source protection.
Distilled water is produced by boiling water and collecting the condensed steam, resulting in water largely free of dissolved solids. It is suitable for specific uses like medical devices or steam irons, rather than regular drinking. Purified water undergoes extensive treatment processes such as reverse osmosis (RO) or deionization to remove impurities and chemicals. RO forces water through a semipermeable membrane, while deionization uses ion-exchange resins to remove mineral ions.
Spring water is sourced from an underground formation where water flows naturally to the Earth’s surface. Mineral water comes from a protected underground source, containing naturally occurring dissolved minerals. Alkaline water has a higher pH level. Well water is drawn from private wells, accessing groundwater, and its quality can vary, often requiring regular testing as it may not be treated like municipal supplies.
Water in Natural Environments
Water in natural settings is categorized based on its occurrence and salinity, defining diverse ecosystems globally.
Freshwater contains low concentrations of dissolved salts. This includes water found in rivers, lakes, ponds, glaciers, and groundwater. Freshwater environments support a wide array of plant and animal species adapted to these low-salt conditions.
Saltwater has a high salt concentration, primarily found in oceans and seas. Brackish water represents a mixture of fresh and saltwater, characterized by an intermediate salinity. This type of water is commonly found in estuaries, where rivers meet the sea, and in deltas, creating unique transitional habitats.
Groundwater is located beneath the Earth’s surface, filling the pores and fractures in underground materials such as sand, gravel, and rock. These water-bearing geological formations are known as aquifers, which can yield usable quantities of water. Surface water refers to any water body found on the Earth’s surface, including streams, rivers, lakes, reservoirs, and wetlands. This water is a primary source for drinking, agriculture, and supporting aquatic ecosystems. Atmospheric water encompasses water vapor, clouds, and precipitation, representing water in its gaseous and suspended forms within the Earth’s atmosphere.
Water by Properties and Use
Water can also be classified by its chemical properties or its status after human use, highlighting its varied impacts and management needs.
Hard water contains high concentrations of dissolved minerals, predominantly calcium and magnesium, acquired as water percolates through geological deposits. While generally safe to drink and a source of these essential minerals, hard water can lead to limescale buildup in pipes and appliances, and may affect skin and hair.
Soft water, conversely, has low mineral content, often achieved through treatment processes that remove calcium and magnesium. Softening can involve exchanging these minerals for sodium ions. Heavy water is a rare form where hydrogen atoms are replaced by deuterium, an isotope of hydrogen with an extra neutron. This type of water is not for consumption and finds specialized uses, such as in certain nuclear reactors.
Wastewater is water that has been used and requires treatment before it can be safely discharged back into the environment. It originates from various sources, including domestic activities, industrial processes, and stormwater runoff.
Greywater is a specific type of wastewater from non-toilet sources, such as sinks, showers, bathtubs, and washing machines. This water contains lower levels of contaminants compared to other wastewater and can often be reused for non-potable purposes like landscape irrigation. Blackwater refers to wastewater from toilets that contains human waste, making it highly contaminated with pathogens and organic matter. Due to its high contamination level, blackwater requires extensive treatment before any potential discharge or reuse.