Maryland Well Yield Testing

How a Septic System Works

A Well Yield Test is a timed-test to determine how many gallons per minute a well system can produce. 

A Well Yield Test will show:

  • A functioning well pump and pressure tank.
  • If a well is running dry or lacks sufficient recuperation.
  • The reserve amount sitting in the well.
  • If the buyers would have to stretch the time between running water: showers, laundry, car washing, dish washer, etc.

Home Land Septic Consulting offers both a full, 3-hour Well Yield Test and a shorter, but less accurate, 1-hour Modified Yield Test.

3-Hour Yield Test


This more accurate, 3-hour test provides sufficient time to run through the reserve of the well, so that the actual amount of water falling into it from the ground can be seen — which by definition, is the well yield.

Modified, 1-Hour Yield Test


This is a shorter, less accurate stress test. It gives the buyer a high level view of the overall performance of the well and pumping system, but may not represent the true statistics of the well, as the 3-hour test will do.

During a Well Yield Test, Home Land Septic Consulting will run water from the well and measure this water in consistent intervals, with five gallons of water being the sample amount at each of these intervals. For best results, water should be taken directly from the pressure tank whenever possible. The last 5-gallon reading is determined to be the “well flow” or “yield” for that well.

Because water runs through the bottlenecks of the well pump and pressure tank, 10-12 gallons per minute is usually the best result for the test. This number may differ from the well yield results produced at the time of drilling, as the bottleneck will have been eliminated.

Baltimore County Regulated Well Yield Test


Official yield tests for private water supplies must be performed under the direct supervision of a Master Well Driller or Pump Installer licensed by the Maryland State Board of Well Drillers, or a Master Plumber licensed by the Baltimore County Plumbing Board.

Yield tests for existing wells in which a submersible pump has been installed and connected to a water distribution system may be performed in accordance with the following procedure:

  1. The contractor performing the test shall provide a testing manifold consisting of an inlet for connection to the pressure line from the well and a tee with a pressure gauge graduated with intervals of at least 2 pounds per square inch (psi) and capable of measuring up to 200 psi.
  2. The testing manifold must be connected so that the pumping switch mechanism is by-passed.
  3. The pump should be turned on and the manifold valve opened completely. Time, flow rate, and pressure readings must be recorded every 15 minutes.
  4. If the water level is drawn down to the pump intake; turn the pump off and record the time. Wait a set period of time (15 minutes); turn the pump back on and measure the discharge of the water until the water level is drawn down to the pump intake again. Record the time and repeat this process at least three times to determine the recovery rate (well yield). The well yield is determined by dividing the average discharge (in gallons) by the average interval (in minutes) between each time the pump was shut off.
  5. For well yields less than 4 gallons/minute, the yield test shall continue by valving down the discharge to the approximate well yield determined in step (4) and recording the flow rate and pressure every 15 minutes until six hours has passed from the commencement of the test.
  6. For recovery rates of 4 gallons/minute or greater, testing may be terminated after three hours if:
    1. The water level is determined to have dropped no greater than 200 feet through the duration of the test; or
    2. The discharge pressure does not vary by more than 5 psi.

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Did You Know?

A typical family of four uses approximately 250 gallons per day.