Surface water collects on the ground or in streams, rivers, lakes, reservoirs, or oceans. It is replenished by precipitation and lost through evaporation and seepage into groundwater supplies. Groundwater collects in aquifers, underground layers of water-saturated rock and sediment. Groundwater is usually obtained by drilling wells.
Water sources can be contaminated by human and natural activities, contributing to sickness and disease from bacteria, viruses, and other pathogens. Public drinking water systems use several treatment methods to provide safe drinking water. Methods used to purify water include:
physical processes such as filtration, sedimentation (allowing particles suspended in water to settle out under the force of gravity), and distillation (converting liquid to vapor and back to liquid again to separate it from contaminants)
biological processes such as the use of microorganisms to remove pathogens in slow sand filters or biologically active carbon
chemical processes, such as the addition of chlorine
Water scarcity refers to the long‐term unsustainable use of water resources. Water scarcity is driven by two phenomena: the increasing use of freshwater supplies and the depletion of usable freshwater resources.
Economic water scarcity results from the ineffective management of otherwise sufficient available water resources. According to the United Nations Development Programme, this is a frequent cause of water scarcity, as most countries have enough water to meet their needs but lack the means to provide it in an accessible manner.
How do we protect our water supply?
Approaches that reduce the consumption of water or replenish fresh water can help protect our water supply. Protecting water sources from contamination also helps protect living things that rely on that water and reduce treatment costs. Individuals and major corporations can implement policies and standard practices to conserve water, such as those recommended by the EPA.
New technologies also can mitigate the impact of drought or water scarcity. Approaches include new ways to make water use more efficient; the desalination of ocean water; improved irrigation and agricultural practices; improved water catchments (areas where water is collected by the natural landscape) and harvesting; and novel methods to recycle or treat wastewater. Caltech investigators are contributing to these efforts with innovations such as a solar-powered toilet and micro-architected materials that can collect fog or generate and collect steam for drinking.
Scientific, technological, and policy solutions for protecting access to water rely on precise measurement and monitoring of underground aquifers, snow, and shorelines.
Caltech researchers and engineers on campus and at the Jet Propulsion Laboratory (JPL) collect this data from ground- and space-based instruments, and they are developing machine-learning methods to combine disparate measurements. For example:
Caltech geophysicists, including Resnick Sustainability Institute researcher and JPL chief scientist Mark Simons, are applying satellite radar technology to track changes in the terrain of Southern California as a result of water flow in and out of aquifers, helping to inform water management districts about the impact of the region's water use on those aquifers.