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Water Flow and Yield Testing

   Homes in rural areas often rely upon a well or spring for drinking water. When buying a home without access to a municipal water supply, you should consider having the water flow tested to determine if the water supply will meet the needs of the household. Nothing is more disheartening than running out of water, or buying a home and then discovering that you will need to have a new well drilled. Water Flow and Yield Testing takes some of the guesswork out of that equation. While the test only establishes the reliability of the water supply at the time of testing, it can give a home buyer some indication of the volume of water at hand.

When is Water Flow Testing Needed?

   Let's say that you're buying a home for your family of 5. The home has been occupied by a single person for the past 15 years, and the owner states that he has never had an issue with the water supply. That may be true, but one person uses much less water than a family of 5 would.
   Most people underestimate the volume of water needed for a household. Showers, dishwashers, drinking water, cooking, laundry, and bathroom facilities all add up to a staggering amount of water usage. The average person uses 80-100 gallons of water per day. Multiply that by your family of 5, and your daily water usage could exceed 500 gallons per day. Beginning to see the need for water flow testing?
   The test can be conducted by a home inspector, and is an inexpensive way to find out if the home has an adequate water supply.
   Before commissioning a water flow test, discuss it with your real estate agent and the home seller. You will need to establish the rate of the draw and how much water will be drawn, and you will need the home seller's permission to have the test done. In my experience, the seller usually agrees to the test, since refusing to allow the test may kill the sale. Water flow testing is not without risk; all parties should be aware that pumping a drilled well dry can collapse the water reservoir beneath it, leading to a potentially costly dilemma.

How is a Water Flow Test Conducted?

   Water is drawn from an exterior hose bib or any water outlet in the home, and the rate of water flow is measured. The water should be directed well away from the home with a length of garden hose whenever possible, since dumping hundreds of gallons of water near the foundation of a home could flood the basement or damage a basement wall. It is also a bad idea to direct the water into or over the septic system or leach field, which can saturate the waste system and cause backups.
   The flow can be measured with a calibrated pail or a water flow meter. Using a flow meter is recommended so that the water pressure can be monitored as the test is conducted. Drawing water at a pressure exceeding 30 PSI can damage a water pump, so it is best to keep the pressure lower. The home inspector will establish how much water is being drawn per minute, and this rate is multiplied by the draw time to determine an hourly draw rate and a total of the water volume in that hour.

For example:

3 GPM drawn x 60 minutes = 180 GPH

   Three GPM (gallons per minute) is a good baseline rate and will not normally put a huge strain on the water pump or plumbing fixtures. The water is usually drawn for a 1 to 2 hour period (or whatever time period you've agreed upon with the seller). A home inspector will sometimes run the water flow test while performing the  home inspection.
   During the course of the test, the water flow should be monitored and re-measured every 15 minutes to make sure that a constant flow rate is maintained. If the well runs dry during the test, it can burn out the water pump or collapse the water reservoir, so it is important to keep an eye on the water flow.

What Does the Water Flow Test Establish?

   First, let's look at what the test is actually TESTING.
   Most drilled wells use a metal casing that is driven into the ground as the well is drilled. As the well is being pumped out during and after the drilling process, water is drawn from the bottom of the casing along with dirt, sand and debris. As this material is drawn out, a reservoir is formed beneath the casing which holds a certain volume of water.
   During the course of the water flow test, this reservoir is pumped out and the water is replenished by water moving into the reservoir from the area around the foot of the casing.
   So to clarify...pumping 300 gallons of water from a drilled well does NOT mean that there is 300 gallons of water sitting at the bottom of the well at all times. The reservoir may only hold 15 gallons at any given time, but it is refilled again and again as water is drawn out.  The same thing applies to a dug well. The concrete tiles of a dug well may hold 150 gallons or more, and as water is pumped out, more water enters the tiles from the surrounding water table.  
   Therefore, it can be said that the water flow test actually measures the rate of recovery of a water supply. The faster the recovery, the faster that water can be drawn from the source. If a well runs dry during the course of the test, then it may have a poor recovery rate and may not be a reliable water source for the household.
   It should be noted that when a water flow test is conducted, it only indicates the water recovery rate at the time of testing. The test can not determine the recovery rate or reliability of a water source at any time in the future, since so many factors can influence the volume of water at hand. Drought, periods of heavy rainfall, excavation in the area, and diversion of ground water sources can all affect the water supply.



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