There are three main types of water: surface water, groundwater, and seawater.
Surface water includes fresh water from lakes, rivers, and streams. It also includes brackish water, which is a mix of fresh and salt water. Groundwater is the water that seeps into the ground and collects in aquifers. Seawater is the salty water found in oceans.
Surface Water
Surface water makes up the majority of the world’s supply of fresh water. It is constantly replenished by precipitation, such as rain or snow. Surface water is often contaminated by pollutants from humans or animals that live nearby. Treatment methods for surface water must remove these contaminants before it can be used for drinking or irrigation.
Groundwater
Groundwater is an important source of fresh water for many communities around the world. It is hidden underground in aquifers—porous rock formations that hold groundwater in storage until it’s needed. When wells are drilled into an aquifer, groundwater can be pumped out for use. Because groundwater isn’t exposed to the atmosphere, it is less likely to be polluted than surface water; however, it can still become contaminated by chemicals that leach through the soil into aquifers. Aquifers can also be depleted if too much groundwater is pumped out faster than it can be replenished by rainfall or snowmelt infiltrating back into the ground.
Seawater
Seawater makes up 97% of all the Earth’s waters but only 3% of its total freshwater supply because it contains high levels of dissolved minerals—primarily salt—that make it unsuitable for most human uses without being desalinated first. Some industries do take advantage of seawater’s other properties, such as its heat capacity (the ability to store heat), which helps power coastal desalination plants and geothermal power plants; its density (heavier than freshwater), which drives ocean currents; and its mineral content (including magnesium, potassium, and iodine), which is harvested to create certain products like table salt, cosmetics, and paper