The term “types of water” refers to how this compound is classified based on its source, the concentration of dissolved materials, and its ultimate application. These classifications are important because the varying qualities and compositions of water directly influence its suitability for human consumption, industrial processes, and environmental health. Understanding these distinctions helps clarify why water from a tap, a bottle, or the ocean behaves so differently.
Water Defined by Mineral and Ion Content
Water’s interaction with the geology it passes through determines its mineral and ion content, leading to the classification of hard or soft water. Hardness is determined by the concentration of dissolved divalent metallic ions, primarily calcium (Ca2+) and magnesium (Mg2+). When water percolates through deposits like limestone or chalk, it dissolves these minerals, forming hard water.
Hard water causes practical inconveniences, such as the formation of limescale deposits on heating elements and plumbing fixtures. These deposits, often calcium carbonate, are left behind when the water evaporates or is heated, reducing the efficiency of appliances. Furthermore, the divalent ions react with soap, forming an insoluble precipitate known as soap scum, which inhibits lathering.
In contrast, soft water contains a very low concentration of these dissolved metallic ions. Rainwater and purified water are examples of naturally or artificially soft water, as they contain few dissolved ions. Soft water readily forms a lather with soap and does not lead to the buildup of scale in pipes and appliances.
The process of water softening is commonly employed to mitigate the effects of hard water in homes and industry. A frequent method is ion exchange, where calcium and magnesium ions are exchanged for sodium ions, which do not cause soap scum or scale. This treatment is necessary in industrial applications, such as cooling towers and boilers, where mineral buildup can cause equipment breakdowns.
Global Water Types Based on Salinity
Globally, water is categorized based on its salt concentration, measured in parts per thousand (‰). The vast majority of the planet’s water, over 97%, is classified as saltwater, found predominantly in oceans and seas. Saltwater has an average salinity of about 35‰, consisting mostly of sodium chloride.
Freshwater is defined by its low dissolved salt content, typically having a salinity of less than 0.35‰. This water is suitable for most life and human uses, though it only accounts for approximately 2.5% of the total water on Earth. Most freshwater is locked away in ice caps, glaciers, and deep groundwater, with only a small fraction available in rivers and lakes.
A third classification is brackish water, which represents an intermediate mixture between saltwater and freshwater. This water type has a salinity level often ranging between 0.5‰ and 30‰. Brackish conditions are typically found in estuaries, where river water mixes with the saline water of the sea.
Categorizing Consumer Bottled Water
The bottled water sold to consumers is classified under specific regulatory standards that define its source and treatment.
Purified Water
Purified water is often sourced from municipal supplies, meaning it starts as public drinking water. It is then highly treated using processes like distillation, deionization, or reverse osmosis to remove minerals and contaminants.
Spring Water
Spring water must originate from an underground formation from which water flows naturally to the Earth’s surface. Regulations require that this water be collected either directly at the spring or through a borehole that taps the feeding formation. The water must maintain the same properties as the natural spring water, although some treatments are permitted.
Mineral Water
Mineral water is distinguished by its consistent level of naturally occurring dissolved solids, requiring a minimum of 250 parts per million (ppm). The minerals and trace elements must come from the protected underground source and cannot be added later. This consistent natural composition differentiates mineral water from other types.
Artesian Water
Artesian water is collected from a confined aquifer, a water-bearing layer under pressure. When the aquifer is tapped, this natural pressure pushes the water up the well, sometimes reaching the surface without mechanical pumping. This classification defines the source rather than the treatment process.
Water Types Based on Intended Use
Water is classified based on its safety and intended application, especially in the context of wastewater management. Potable water serves as the baseline, meaning it is safe for human consumption, cooking, and hygiene use. This classification requires the water to meet stringent quality standards for microbial, chemical, and physical contaminants.
Water that is no longer potable but can still be reused for certain applications is categorized as gray water. This includes wastewater from sources like showers, bathtubs, sinks, and washing machines, which does not contain fecal contamination. Gray water is safer to handle and can be treated relatively easily for non-potable uses, such as landscape irrigation or toilet flushing.
In contrast, black water is defined as wastewater that has come into contact with human waste, primarily originating from toilets and urinals. Due to the presence of pathogens and high levels of contamination, black water is considered hazardous and requires extensive treatment before it can be safely discharged or reused. Mixing gray water with black water results in sewage, which must be routed to a centralized treatment facility.