Water Well Journal
Issue link: http://read.dmtmag.com/i/573697
What is adequate quantity? Many people, including experienced engineers and water system designers, are often amazed at how little water people actually use for personal uses every day. The proper use of this information can assist designers when planning water systems in areas with low-producing wells. In past years, I successfully designed domestic water sys- tems based on individual water usage of 100 gallons per day with well yields as low as ½ GPM, even for a family of four to five. Granted, in these situations the family must learn and observe new rules in their use of available water, but it can be done. In more recent years, I've been amazed at how much the typical residence can cut back and conserve water when needed—especially in public water systems or those that charge a fee for water. Although I would like to state this observation is the result of actual conservation attitudes, the actual truth is more likely financial. That's because most of the lower per capita (per person) water usage is typically the result from lessening water consumption due to higher water rates. The typical American generally uses between 10-60 gal- lons of water per day for individual uses. This includes all uses related to personal hygiene, bathing, drinking water, and cooking. It doesn't include long-duration showers, taking more than one bath, or irrigation. It is a fairly broad spread attributable to various factors such as water system pressure, personal and family water use practices, water fixture output, water palatability, economic conditions, and, of course, the cost of water. Even if a much higher daily volume of 100 gallons per day per person is assumed, a family of five will typically use only a total of 500 gallons per day. Irrespective of grounds irrigation, stock watering, and other type of mostly rural uses, this relationship seems to hold true for most classes of water consumers in both urban and rural settings. Obviously, in the case of individual water sys- tems any lack of cooperation within the family, water system or fixture leakage, or additional decline of well yield will greatly impact the water system. But the point to be gained is lowering water consumption can be done! Most of the water (75% to 90%) used by a typical family is usually consumed over a four-hour period of the day. Studies have shown the majority of a family's daily water usage is consumed between the morning hours of 6 and 8 a.m. and the evening hours of 6 and 8 p.m. In order to accommodate this need and provide a reason- able margin of safety, a properly designed water system should be able to provide an entire day's water supply in a two-hour (120 minutes) period. Therefore, for our theoretical family of five who uses 500 gallons of water per day, the water system, through a combination of storage and pumping, should be designed to produce 500 gallons divided by 120 minutes—a minimum of 4.2 gallons per minute (GPM). This value closely approximates the 5 GPM minimum flow rate for four continuous hours that many lending agencies re- quire for a home loan, and also gives you an idea where this number first came from. Many lending institutions, recogniz- ing a family's daily water usage is far less than the former minimum of 1200 gallons per day, will provide financing for properties with well yields as low as 1-2 GPM. In these cases, however, they will almost always require additional water storage before lending the funds. The required volume of on-site storage varies greatly re- gion to region, lender to lender, and will also be affected by any government agency, such as the Federal Home Adminis- tration, that will guarantee the loan. In all cases, it is impera- tive the specific requirements from the lender, as well as any guarantor, be determined before proceeding with a specific water system design or construction. Typically, a well with a sustained yield of 2 GPM will re- quire between 1200-2000 gallons of active storage. In these cases, the well discharges water into an atmospheric storage tank (which is usually constructed from concrete, steel, or plastic) and a booster pump then re-pumps and delivers the stored water to the home. Additional water demands—landscape or turf irrigation, water filter backwash, hot tubs, large bathtubs, saunas, or water source heat pumps—will often greatly increase the de- mands placed on the well and must be individually consid- ered. In many regions of the country, irrigation water can be reclaimed water or even collected rainfall and reused. The important thing to remember is you must apply good design techniques based on your specific region, the customer's spe- cific water use characteristics, lending agency requirements, local factors, and reliable well capacity to each design. In all situations, I highly suggest an extended well produc- tion test be performed on each marginal well before commit- ting to use of the well. Typically, the lower the production the longer the well test should be—with periods of up to 24-48 hours recommended for low-producing wells of 2 GPM or less. In many cases the storage of the wellbore can be factored into the ultimate well production, resulting in the ability to lower the volume of water storage needed in above-ground vessels. What is fixable quality? Often, low-producing wells are inherent troublemakers due not only to their low production but also to water quality issues. Generally in areas of low-producing wells, drillers will be forced to develop wells from formations with inferior water quality, such as shale and sandstone, and at depths ENGINEERING from page 52 DACUM Codes To help meet your professional needs, this article covers skills and competencies found in DACUM charts for drillers and pump installers. DO refers to the drilling chart and PI refers to the pumps chart. The letter and number immediately following is the skill on the chart covered by the article. This article covers: DOA-3, DOA-5, DOB-1, DOB-2, DOB-3, DOB-4, DOG-9, PIA-3, PIA-4, PIB-3, PIB-6, PIC-1, PIE-21, PIF-1 More information on DACUM and the charts are available at www.NGWA.org. 54 October 2015 WWJ waterwelljournal.com