What Is a Well Flow Test?
A well flow test measures the sustained yield of a water well in gallons per minute (GPM). In Oregon, this is not legally required for a residential sale, but most lenders require one, and any buyer of rural property should insist on it. The test typically runs for two to four hours, drawing water at a steady rate while monitoring the static water level and the recovery rate.
What GPM Do You Need?
The general rule for a single-family home is a minimum of 5 GPM sustained. However, if you plan to irrigate a garden, water livestock, or run an accessory dwelling unit, you may need 10 GPM or more. Properties below 3 GPM often require a storage tank and pressure system, which adds $5,000 to $15,000 to your setup costs.
Red Flags to Watch For
A well that recovers slowly after drawdown may indicate a declining aquifer or seasonal limitations. Wells drilled during wet months can test well in spring and fail in August. Always ask for historical flow data if available, and request a test during the driest part of the season when possible.
Oregon Well Regulations
The Oregon Water Resources Department (OWRD) maintains well logs for every permitted well in the state. You can look up any property’s well log online for free. The log shows depth, casing, and the original driller’s reported yield — though yields can change over decades.
What I Tell My Clients
If a property has a well, the flow test is non-negotiable. I schedule it early in the inspection period so we have time to negotiate or walk away. A bad well does not always kill a deal — sometimes the seller will drill a new well or credit the cost — but you have to know what you are working with before you commit.
