Hello Mark

Saw your response to a well flow rate question and thought you might be able to help answer a question to which, as of yet, I can’t get a sensible response.

When a well flow rate is tested at a tap or spigot and timed as it runs into a pail (for simplicity sake) and a certain flow rate is recorded. Let’s say 8 GPM. Then you test half an hour later and it is down to 4 GPM. What makes it change? The well hasn’t run dry. The pump (submerged) is still under water. What factor(s) can cause less water to run out of the tap as long as there is still water above the pump in the well casing? Can’t get my head around that … hope you can help.

Thanks

Glenn

Glenn,
Most wells have a resevoir tank inside the home that holds a significant amount of water. Before actually measuring, the water should be run for a period of time to empty that tank. If the first measurement is 8GPM then that water isn’t likely coming directly from the well but from the tank. Once the tank is depleted, then the water coming out of the spigot is coming out at the same rate that the pump is re-plenishing it.  So in your example the well is actually producing 4 GPM.

Hope that helps.

Mark

Mark Nahrgang is the owner of Kingdom Inspection Network Group – St. Louis and is a professional NACHI certified building inspector in the St. Louis metro area. Mark performs home inspections as well as commercial inspections throughout St. Louis and St. Charles County. If you are looking for a thorough and qualified St. Louis area home inspector, use the contact information on this site to contact Mark regarding available services.

Filed under: Wells/well water