Green Risks: Testing the Stabilized Yield in a Well

Wednesday, November 5, 2025

Testing the Stabilized Yield in a Well

I have recommended that when buying a home with a well you have at least a 6 gallon a minute stabilized yield. The reason you want to make sure you have at least a 6 gallon a minute stabilized well yield/flow is to be sure that the water supply is adequate to do laundry and have everyone shower in the morning. The rule of thumb is 6 gallons/minute is an adequate yield to supply on-demand water for a typical household (some places they use 5). It really depends on how many people and bathrooms and how deep the well is.

So let’s talk about this. First you begin by taking a look at the well completion report on file with the county health department. It shows how deep the well was drilled, where water was found and the stabilized yield. The minimum you should look for are:

The well stabilized yield should be greater than or equal to 6 gallons/minute
The well should be drilled and more than 100 feet below grade (deep)

Over time the yield of most wells falls and what was an adequate well 20 years ago may not be now. In some geologies the well yield can fall by 50% or more in 20 years, and a low yielding well may be drying out after 20 years. It is also possible that over the years the groundwater level has fallen below the level of water zones in your well because of overuse of the groundwater aquifer or reduced recharge to the aquifer. Nationally, groundwater levels are falling.

In order to actually measure the stabilized yield on a well, you need a licensed well driller with the right equipment test the yield of the well for you and here is why. First, any sane person would not let some random Stanger open their well. Especially one with a YouTube video as research. Anytime you open a well you must thoroughly disinfect it. To properly disinfect a well is major pain in the butt and in my case, it can take up to a week before the rust color and chlorine are thoroughly out of the well water. I would no sooner let you open my well than cut a piece of the drywall out to look at the insulation.

As a review, you disinfect a well by circulating a concentrated chlorine solution throughout the system. The level of chlorine to use is between 50 ppm and 200 ppm (parts per million) depending on which University extension office is asked. Once the chlorine solution is well mixed (this can take a few hours), you seal up the well and system for 12-16 hours then you flush the well.

If you have not recently chlorinated the well a bunch of orange and brown gunk will come out of the well during the flush. Because I chlorinate my well every few years, I only get orange/ brown tinged water. To flush my well, I run the hoses to a non-sensitive area for at least an additional 24 hours till it runs clear and the chlorine level drops towards non-detect. It can take an additional week for my well to clear of every trace of chlorine and discolored water.

Second, you need to pull the pump and use a specialized pump and an appropriate power source to perform an actual pump test. Otherwise you can only test a yield less than your pump rate. Read the Virginia guide here. In addition, in an established neighborhood it is possible that you will impact neighbors. The low tech method is probably better for these purposes.

Using the hoses is one way to make sure the well yield is adequate. The rate at which a hose runs is impacted by the length of the hose, but it is typically about 3 gallons a minute at normal garden length (you can easily check that with a stop watch and a 1-gallon bucket- 60/seconds to fill bucket= rate). If you are running two hose you are running off about 6 gallons a minute. To make sure that your well is recharging at least at that rate you need to account for the water in the well itself.

The well column holds water. If the well was drilled to 150 feet below grade and the static water level is 43 feet below grade, there is about 156 gallons of water stored in your well. [you calculate the gallons of water in a well by is:

volume = 𝜋×𝑟2×ℎ×7.48

where 𝜋 equals 3.14159
radius is one half the diameter of the well in feet
height is the depth of the well minus the static water level and
7.48 is the number of gallons per cubic foot.

Using my well as an example, it is 150 feet deep and when measured 5 years ago had a static water level of 43 feet below grade so that mean there is about 156 gallons of storage in my well. If I ran my hoses for 5 hours I would have used 1,800 gallons of water. This is enough for our purposes. You need to check the hoses every 20 minutes to make sure they are still running and that the rate of flow remains constant (bucket and stop watch). If my well did not run dry in all that time it is a safe bet that there is plenty of water to run a household.

Back in 2020 I replaced my pump and pressure tank. I wanted to make sure I had adequate recharge to size up my pump. The only way I could do it was to measure off the pump itself. These days you can measure the static water level using a sonar gun to bounce the signal off the water. The well guy had one. My static water level in early March of 2020 was 43 feet below grade. This is 13 feet lower than when the well was first finished.

If you pull your pipe out of well bringing the pitless adaptor to the surface (using the correct tools your could actually pump the water out of the well at the rate the pump runs. Most residential wells use 10 to 15 gallons a minute. After putting the new pump in the well, the well guy ran the pump for about two hours. I measured the flow off the pump at about 4 seconds to fill the gallon bucket. At that flow rate it would only take two hours to run 1,800 gallons. Which it did. Before he sealed up the well, he once more measured the static water level- still at 30 feet below grade. That proved that my well recharge rate exceeded the pump rate. Good to go with my new pump after letting the well settle and chlorine shocking the well to disinfect it. No one but me or a licensed and vetted well contractor ever messes with my well.