By Jan TenBruggencate
Advertiser Staff Writer
Much of the rain that falls on the Islands washes down into streams and eventually into the sea, but a large proportion soaks into the ground, eventually to become part of the state’s valuable supply of groundwater.
This represents water, sometimes filtered through thousands of feet of soil, sand and rock, that is available to wells as some of the purest drinking water we have.
It also is water capable of being contaminated — by waste oil dumped on the ground, by chemicals used in agriculture, and by a range of chemicals that are washed out onto the fields and gullies of the Islands.
A series of studies in Europe and the United States is finding that some water supplies are contaminated with antibiotics. Health officials are concerned that excessive use of antibiotics is allowing them to enter the environment, where disease organisms are able to evolve into antibiotic-resistant forms.
Contaminants normally are found in shallower water systems, but with time, they could seep into the deeper water sources upon which many communities rely.
The National Ground Water Association will highlight the values of and risks to groundwater during National Groundwater Awareness Week, May 6-12.
Groundwater isn’t locked up forever under our volcanic Islands. Some of it seeps into valleys to join other waters and form streams. Many of Hawai‘i’s streams are primarily spring-fed, meaning they get almost all their water from underground sources.
Some of the water, trapped at high elevations by geological formations called dikes, pops out of the sides of rock faces and cliffs, where it is visible in the form of patches of bright green vegetation that thrive on the steady supply of moisture.
Some seeps into wetlands, creating a range of habitats for birds, fish and water-dependent plants.
Some seeps into the nearshore waters, changing the salinity and creating microhabitats for forms of marine life that prefer things a little less salty than what’s normal in the ocean.
Despite the apparent prevalence of lakes and rivers, the National Ground Water Association estimates that, excluding polar ice caps, 90 percent of the fresh water on the planet is groundwater.
"In the U.S., 47 percent of the population depends on groundwater for its drinking water supply, and several large U.S. cities use it as the chief source of water. In many parts of the world, it provides the least-expensive supply of quality water for human use," the association said.
For more information on groundwater and the National Ground Water Association, call (800) 551-7379, or visit the organization’s Web site at www.ngwa.org.
Jan TenBruggencate is The Advertiser’s Kaua‘i bureau chief, and its science and environment writer. You can call him at (808) 245-3074 or e-mail jant@honoluluadvertiser.com.
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