How to Test a Well for Gallons Per Minute (GPM): A Comprehensive Guide

 

If you rely on a well for your water supply, understanding its production flow rate or production in gallons per minute (GPM) versus the well pump’s capacity (GPM) is essential. Knowing your well pump’s GPM can help diagnose efficiency problems and knowing your well’s production rate  helps you gauge its useability, plan water usage efficiently, and detect potential issues. In this blog, we’ll walk you through the steps to test a well pump system for gallons per minute, also known as water well flow rate testing.

 

Why Test Your Well’s GPM?

 

Before we dive into the testing process, let’s understand why it’s crucial to determine the flow rate of your well pump and your water well production rate:

 

Water Supply Assessment: Knowing your well’s GPM helps you assess the adequacy of your water supply. It ensures you have enough water for daily needs, irrigation, and other purposes.

 

Detecting Problems: Monitoring your well pump’s flow rate can help you identify issues such as pump efficiency losses, mineral buildup in the well slowing well production, or declining water levels.

 

Planning Efficient Usage: Understanding your well’s GPM allows you to plan water usage more efficiently, preventing overuse and potential well depletion.

 

How to Test Your Well for Gallons Per Minute

 

Materials You’ll Need:

 

Measuring Container: You’ll need a large container or bucket with precise measurements marked on it. The best option is a 5 gallon bucket and use the upper most rim as the 5 gallon mark.

 

Timer or Stopwatch: To measure the time it takes to fill the container.

 

Steps to Determine Your Well’s GPM:

 

Step 1: Assess The Condition of the Well Pump System – Ensure your well pump system is functioning correctly, and there are no visible leaks or issues.

 

Step 2: Choose a Test Location – Select a location where you can easily access water from your well, such as a hose bib or a faucet. A frost free, yard hydrant is the best option if you have one, as it will flow the most water out of it. Ensuring that the pump stays running continuously is key. If the pump is able to pressure up and shut off, your flow test will be inaccurate as the well will start to recover during this time, even though you still have water flowing. Using a hose bib on the house is suitable, but you may need to run two at a time to keep enough water flowing to prevent the system from pressuring up and shutting off during the test. 

 

Step 3: Measure the Flow Rate – Place your measuring container under the selected faucet or hose bib. Open the faucet or hose bib to its maximum flow. Start the timer as you begin filling the container. Stop the timer as soon as the container is full, recording the time in seconds.

 

Step 4: Calculate GPM – To calculate your pump’s GPM, use the following formula:

 

GPM = (Container Size in Gallons) / (Time in Seconds / 60) or 300 / seconds to fill the bucket

 

This GPM is what your well pump is capable of pumping. The next thing to do is to determine what the well will produce while you are pumping this rate.

 

Step 5: Continue Running- Continue letting the water flow, taking GPM readings every 5 minutes for the first half hour and then every 10 minutes thereafter. It is typical to have the GPM rate of the pump slow down as the water level in the well lowers from being pumped. The goal is to determine if the pump will evacuate all of the water out of the well or stabilize at some point to where the amount of water being pumped doesn’t continue to drop and is equal to the amount of water coming into the well. At either point, the amount of GPM being pumped is close to or equal to the actual production rate of the well itself. 

 

Interpreting the Water Well Production Rate Results

 

1. A GPM rate of under 5 GPM is considered low and may indicate the need for well cleaning to remove mineral deposits that are restricting the flow of water into the well or the need for a cistern. All of this depends on how the water is being used and if it is enough for these uses or not. Some people are able to easily live on less than 5 GPM from their well. Others are not. 
2. A GPM rate of 5-15 GPM is typical for most residential wells and meets the water needs of an average household.
3. A GPM rate above 15 GPM is considered high and signifies a well with excellent water production. In Colorado, most domestic well permits only allow for a maximum of 15 GPM to be pumped from the well. 

 

By following these steps, you can determine your well’s GPM and take steps to ensure a consistent and reliable water supply for your home. Water well production rate testing is a valuable tool for every well owner, helping you make the most of your precious groundwater resources. If you have concerns about your well’s flow rate, encounter issues during testing, or are curious about general water well services, call Barnhart Pump Co. at 719-781-2533 for further evaluation and maintenance.