1 WD DWGB18 2010 Recommended Minimum Water Supply Capacity for Private Wells One of the most important factors to consider when planning to purchase or build a home is the adequacy of the water supply. The amount of water available to the home can be as important as the quality of the water. How much water is adequate for a private domestic supply is a commonly asked ques tion of DES and the Water Well Board. Available water supply is a function of both the recovery rate and the storage volume of the well. These two factors contribute to the actual capacity of the supply particularly if the well recovery rate is low. A standard 6inch di ameter drilled well can store 1½ gallons of water per foot of well depth. The actual volume of water in storage will depend on the water level in the well and the pump setting depth. The Water Well Board suggests that a minimum water supply capacity for domestic internal household use should be at least 600 gallons of water within a two hour period once each day. This is equivalent to a flow rate of 5 gallons per minute (gpm) for two hours. Some homeowners may find this amount to be less than desirable depen ding on the size of the family or if outdoor use is a requirement. Water supply capacities less than this amount may be considered a hardship by many homeowners. In addition, the New Hampshire Water Well Association and the Board recommend a flow rate of 4 gpm for a period of four hours as an optimum water supply capacity for a private domestic supply. This volume is equivalent to 960 gallons of water within a fourhour period and should be adequate for all indoor domestic use as well as a modest amount of outdoor use. The following tables were developed to assist readers to interpret the recommen dations above. In both tables, the overall yield is the sum of the aquifer yield to the well and the available well storage. The tables presume a pump setting of 20 feet above the bottom of the well and a static water level of 20 feet below the ground surface. Minimum Capacity The values in Table 1 provide a yield of 600 gallons of water to the home during a period of two hours of pumping.
2 Tab le 1. Supply 600 gallons in Two Hours Required Well Depth (Ft) Sustained Well Yield (GPM) 400 0.5 1 360 1.5 320 2 280 2.5 240 3 200 3.5 160 120 4 80 4.5 5 Optimum Capacity The values in Table 2 provide a yield of 960 gallons of water to the home during a period of four ho urs of pumping. Table 2. Supply 960 gallons in F our Hours Sustained Well Yield (GPM) Required Well Depth (Ft) 0.5 600 1 520 440 1.5 360 2 2.5 280 3 200 3.5 120 4 Contact a licensed water well contractor or licensed pum p installer for information about pumping tests and available options for increasing the capacity of inadequate supplies. Al so see f act sheet WDDWGB116 at 116.pdf http://des.nh.gov/organization/commissioner/pip/factsheets/dwgb/documents/dwgb For further information about water supply and wells you may call the Water Well Board at (603) 2711974 or the DES Drinking Water and Groundwater Bureau at (603) 2712513 or go to their websites located at http://des.nh.gov/organization/divisions/water/dwgb /wwb/index.htm and http://des.nh.gov/organization/divisions/water/dwgb /index.htm , respectively. Rev. 8/10/2010
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