Will a drought impact ground water quality?

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First of all, it's important to define a drought. A public water supplier is concerned with two aspects of drought. The first is the physical effect on water quantity and water quality (supply). The second is how the drought affects consumers (demand). A drinking water system will be affected by drought when decreasing supply intersects increasing demand. For the purposes of this assessment, drought is defined as a deficit of precipitation sufficient to create stress on and competition for otherwise adequate drinking water supplies.

One of the best studies of how drought affects a water supply is a study recently performed by Maine. Maine experienced the worst drought in over thirty years during 2001 and 2002. Water in streams, lakes, and groundwater dropped to record-low levels. Thousands of private wells went dry, and many public water systems were forced to implement water use restrictions and tap into back-up supplies. The drought exposed vulnerabilities in the state's public water supply, highlighting a need for water use planning and management even in a "water-rich" state like Maine.

Not all public surface water systems experienced problems, even in areas where the drought was severe. Small, shallow lakes that were already being pumped close to their safe yield were the most vulnerable surface water supplies. These systems were located in the coastal region and other areas where seasonal tourism and residential development increase water demand, suggesting that surface water systems with these characteristics are most likely to be affected by future droughts. This document highlights the effects of the drought on Maine surface water supplies and discusses ways that managers of vulnerable systems can prepare for future drought and climate variability.

Although New England is considered to be "water-rich," Maine has experienced several significant drought periods, the most recent in 2001, the driest year since records began in 1895. The severity of the drought varied across the state, with northern Maine experiencing the driest conditions. Lakes, streams, and groundwater were at record low levels.

What were the end results? Public water supplies were affected by the 2001-2002 drought, based on a survey of surface water systems and reports to the Maine Drinking Water Program and Public Utilities Commission. A system was considered affected by the drought if:

  1. water quantity was reduced enough for the system to impose voluntary or mandatory conservation;
  2. the system manager utilized or explored additional or alternative supplies; and/or
  3. the manager expressed concern about the drought's effects on water quantity or quality.

How a particular water supply responds to drought will depend on its size and watershed characteristics, and the relative contributions of precipitation, surface runoff, and groundwater to the overall water budget. Water levels in 2001 were below normal in the majority of public water supply lakes and streams, in some cases at record low levels. Yet only eight surface water systems were considered "affected," meaning they had problems as a result of decreased water volumes. Climate and hydrologic conditions alone were not enough to drive a system to implement water use restrictions.

In general if you are a well-owner and get your water from there, there is no adverse impact on overall ground water quality from a drought. If a homeowner drills a deeper well in response to a drought, the homeowner may end up with more mineralized water. This is because the water has been in the ground longer and may have taken on some of the characteristics of the surrounding rock formations. The homeowner may also gain water quality benefits from a deeper, properly constructed well. These deeper wells are better protected from surface people-related contamination sources, such as septic tank effluent, lawn fertilizer applications or accidental spills.

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