Designing an irrigation system using a private well presents distinct challenges compared to connecting to a municipal supply. City water offers relatively limitless flow and consistent pressure. A well, however, is a finite and dynamic source, meaning the sprinkler system design must prioritize the well’s physical limitations, especially its capacity to deliver water over time. The design process must begin with a comprehensive assessment of the water source to ensure the final system operates reliably without damaging the well or the pump.
Assessing the Well’s Capacity
The foundational step for a successful well-fed irrigation system is accurately measuring the well’s performance metrics: static pressure, flow rate, and recovery rate. Static pressure, measured in pounds per square inch (PSI), is the reading taken when no water is actively flowing, typically close to the pump’s shut-off pressure. This value provides the maximum available pressure before accounting for friction loss or flow demands.
The sustainable flow rate, measured in gallons per minute (GPM), is determined by conducting a flow test, often called a bucket test for residential systems. This involves timing how long it takes to fill a container of a known volume, such as a five-gallon bucket. To get a true reading of the pump’s output at a specific pressure, the test should be performed at a hose bib near the well, ensuring the pump runs continuously during the measurement.
The well’s recovery rate, the speed at which the water level returns after pumping, is the single greatest constraint on system size. If the irrigation system pulls water out faster than the aquifer can replenish it, the well may “draw down,” causing the pump to suck air and potentially fail. For low-yield wells, a professional well yield stress test is necessary to determine a sustainable GPM that will not deplete the well over the long irrigation run times. The final irrigation design must use a flow rate equal to or slightly below this sustainable recovery rate to prevent damage and ensure system longevity.
Integrating Well-Specific Hardware
Specialized hardware is necessary to protect the irrigation system and maximize the well’s usable output because well water often contains sediment and the source is dynamic. The primary component is the pump, selected based on the well’s depth and the required flow and pressure. Submersible pumps are the most common choice for deeper wells, as they push water from below, providing higher pressure and greater energy efficiency compared to above-ground jet pumps.
A pressure tank is a necessary addition to any well system, acting as a pressurized reservoir that stores water and maintains consistent system pressure. This storage capacity prevents the pump from rapidly cycling on and off every time water is drawn, significantly prolonging the pump’s lifespan by reducing wear and tear. The tank uses an air bladder that compresses as water is pumped in, forcing water into the system when needed.
Filtration is necessary hardware, protecting the internal components of sprinkler heads and valves from debris. Well water frequently carries sand, silt, and fine sediment that can easily clog small nozzles. Centrifugal sand separators, like cyclonic models, are effective at removing larger particles using rotational force. Further downstream, a sediment filter, such as a disc or screen filter, may be installed to catch finer particulates, ensuring the water is clean enough to pass through the smallest sprinkler orifices.
Hydraulic Calculations and System Zoning
The design phase translates the well’s measured capacity into a functional irrigation layout through careful hydraulic calculations and system zoning. Hydraulic calculations determine how much pressure is lost as water travels through the pipe, a phenomenon known as friction loss. This loss is a function of the pipe’s interior roughness, diameter, and the velocity and volume of water flowing through it, and it is commonly estimated using charts.
The primary design goal is selecting a pipe diameter that keeps the water velocity below a recommended maximum, typically 5 feet per second, to minimize friction loss and prevent damaging water hammer surges. Using larger-diameter pipes, such as 1-inch or 1.5-inch PVC, for the main lines reduces friction loss substantially, ensuring sufficient pressure reaches the furthest sprinkler heads. The total friction loss, including losses from fittings, valves, and elevation changes, must be calculated to determine the final working pressure available at the sprinkler head.
System zoning is the most constrained aspect of a well-fed system, as the total flow required for any single zone must not exceed the well’s sustainable GPM. If the well’s sustainable flow rate is 8 GPM, for example, every individual irrigation zone must be designed to consume less than 8 GPM. This is accomplished by selecting sprinkler heads and nozzles whose combined flow rate falls under this limit. For example, if the sustainable flow rate is 8 GPM, all zones must be designed to consume less than 8 GPM by limiting the number of heads per zone.
This division ensures that the pump is never overworked and the well is not drawn down faster than it can recover. By calculating the flow demand of each head and grouping them into zones that respect the well’s GPM limit, the designer ensures the entire system operates efficiently within the pressure range provided by the pump and pressure tank. The final step involves selecting nozzles and heads that operate effectively at the calculated available pressure, ensuring proper water distribution and coverage across the landscape.