Groundwater is a source of freshwater collected under the water table of a site. Refreshed and recharged by rainwater that percolates through the soil, it usually carries a rich mineral content and contains various elements ranging from heavy metals such as cadmium, chromium, iron, nickel, copper, manganese etc. as well as decayed organic materials and microorganisms.
Many cities around the world, especially those in water starved regions, pump groundwater up through deep tube wells and treat the water prior to consumption. Water treatment processes used typically follow those for cleaner sources of water such as river water and freshwater reservoirs, and include steps such as: (i) sedimentation, (ii) coagulation, (iii) sedimentation, (iv) fast sand filtration, (v) slow sand filtration, (vi) chlorination, and (vii) ultraviolet disinfection. While the above treatment steps would remove most of the organic, inorganic and microbiological contaminants, they would not be able to cleanse groundwater of some of the most deadly contaminants that linger in polluted soils such as perchlorate, arsenic, chromium, boron, manganese and nickel. Hence, efforts aimed at utilizing groundwater as a source of drinking water faced severe obstacles, primarily in the high cost of treating groundwater for removing all of the heavy metal contaminants. Such treatment would necessarily utilize the high energy consumption and costly processes of hollow fibre membrane ultrafiltration, and non porous membrane reverse osmosis.
Besides difficulty of removing all or most of the heavy metal, inorganic, and organic contaminants from groundwater, another important problem of equal measure that associates with groundwater use as a source of drinking water is land subsidence, which in coastal areas, is further exacerbated by saltwater intrusion. Without the water pressure from a saturated water table, pumping of groundwater would result in progressive subsidence of land, which would result in carve-in of land and destruction of property.
Thus, analysing the problem of whether a city should use groundwater as a source of drinking water clearly points to the inability of current drinking water treatment processes in removing heavy metal contaminants such as chromium, arsenic, nickel and manganese as well as common organic and inorganic contaminants that include boron. Processes able to remove such contaminants would rely on high pressure ultrafiltration and reverse osmosis, which being expensive and hard to institute in impoverished parts of the world, are not available to many communities that rely on groundwater as a sole source of drinking water such as cities in deserts. Having an alternative source of water such as freshwater reservoirs meant that a city does have a choice on drinking water supply. Whether a city decides on selecting groundwater as a drinking water supply route depends on the availability of reverse osmosis technology and the energy and monetary resources able to support it. More importantly, the city would also need to take possible land subsidence from groundwater withdrawal into account.
However, having the requisite water treatment technologies on hand does not necessarily meant that a city should plunge head on into using groundwater as a drinking water source, as expanding the collection of rainwater in freshwater reservoirs is a more viable and cheaper long-term solution to an existential problem. Using rainwater as a source of drinking water would earn token for not incurring lasting damage to the population’s health from drinking groundwater contaminated with trace amounts of neurotoxins such as lead and arsenic, as well as protecting the landscape of the terrain, unimpacted by groundwater excavations. Through the eons of human civilisation evolution, cities and towns are usually built alongside rivers or near freshwater lakes; thus, except for excruciating circumstances where a township emerges from mining of gold, minerals or oil and gas in an area without freshwater resources, do groundwater use becomes a last resort option after extensive treatment, while presence of other sources of freshwater makes groundwater use a non starter.
Category: environment, water treatment, environmental engineering, environmental economics,
Tags: drinking water, trace contaminants, groundwater, arsenic, chromium, heavy metals, boron, manganese, reverse osmosis, perchlorate, ultrafiltration, land subsidence, freshwater reservoir,