Irrigation site survey and available water
Key Takeaways
Record source flow and pressure together under relevant operating conditions.
Survey elevation, exposure, plants, soils, obstacles, and maintenance constraints.
Meter rating, service capacity, pipe velocity, and nozzle pressure are separate checks.
Begin with the landscape
An irrigation design starts with a measured base plan and the planting's water needs. Record beds, turf, trees, paving, buildings, slopes, retained plants, and areas that must stay dry. Identify wind exposure, shade, reflected heat, soil texture, restrictive layers, and infiltration behavior. Draw the property and use constraints rather than assume sprinklers can be placed anywhere along its perimeter.
Measure elevation differences from the proposed source to potential heads and assemblies. A thirty-foot vertical rise costs about thirteen psi of pressure before friction, using 0.433 psi per foot. A long horizontal run creates friction but not that elevation loss. Confusing distance and rise can either oversize the equipment or produce a zone that cannot operate.
Locate utilities and private infrastructure before routing trenches. Consider protected roots, foundations, septic systems, future construction, gate access, and traffic loads. Position valves, filters, controllers, and isolation devices where they can be serviced. A technically correct hydraulic layout can still be unbuildable or unsafe if it crosses a protected feature without an approved detail.
Identify the source
Determine whether water comes from a municipal service, well, pump, storage tank, reclaimed system, or another source. Record meter model and size, service material and diameter, pressure regulation, allowed flow, operating schedule, and any water restrictions. An unrestricted source is not an unlimited source. Well yield and pump capacity must both support the planned duty.
Check potable protection and authority requirements before connecting. An irrigation system with chemical addition or another water source changes the cross-connection assessment. Reclaimed water requires its own identification, permitted use, and separation. Do not connect two sources with a simple selector valve and assume a check valve makes the arrangement acceptable.
Review source reliability and concurrent demand. Domestic fixtures, other irrigation zones, pressure cycling, and seasonal supply changes can reduce available pressure. Design for the specified operating condition and record it. If the owner intends two zones to run simultaneously, the hydraulic analysis must include both rather than assume each operates alone.
Measure a flow-pressure relationship
Measure static pressure with no flow at the identified point. Then measure pressure while a known flow is drawn through the appropriate test arrangement. Use suitable gauges, flow measurement, and safe discharge. A bucket test computes flow from volume and time, but a wide-open hose test without working pressure does not establish the available flow at the nozzle's required pressure.
For example, filling five gallons in twenty seconds gives fifteen gpm: five divided by twenty times sixty. If the source pressure during that test is only twenty psi, the result cannot support a design that assumes fifteen gpm at forty psi. A different controlled test may show ten gpm at forty psi. Record both quantity and pressure instead of selecting the larger flow because it looks favorable.
The measurement location matters. A gauge downstream of the meter and backflow assembly already includes losses through those components at the test flow. Subtracting them again double counts. A reading upstream requires including them in the downstream budget. Sketch the source and test arrangement and label what the reported pressure represents.
Convert findings to design constraints
Set the allowable simultaneous flow using supplier limits, meter/service ratings, measured pressure, pump or well conditions, and required reserve. Then verify distribution piping and equipment losses at that flow. Do not use a universal fraction of meter capacity as a substitute for actual data. Some design references apply a conservative fraction of maximum ratings; the basis and equipment must be known.
Check pressure at the hydraulically controlling outlet, which may be distant, high, or both. Lower outlets may need regulation to avoid misting. A pump can require pressure controls or storage designed for its cycling behavior. Increasing pipe diameter reduces friction but does not correct an inadequate source yield or excessive elevation lift.
Document the survey
Create a concise design-data sheet with date, source, test point, static and working readings, measured flow, meter and service details, elevations, soils, planting needs, and uncertainty. Identify assumptions requiring confirmation before construction. A missing pipe diameter should appear as an unresolved design input rather than an invented value.
Share the constraints with the owner before proposing zones and costs. A limited supply may require more zones, longer available watering windows, lower-flow equipment, or a changed planting plan. Explain that slower application can suit a soil better but may increase runtime. Good survey information prevents purchasing equipment that cannot operate under the actual site's conditions.
Reference table
| Survey input | Design use |
|---|---|
| Working pressure and flow together | Establish usable supply condition |
| Source and test point | Identify losses already included |
| Elevations | Calculate uphill loss and downhill gain |
| Soil and plants | Establish application and schedule needs |
| Utilities and access | Route buildable, serviceable systems |
Five gallons are collected in twenty seconds while source pressure is twenty psi. What can be concluded?
Fifteen gpm is available at any desired pressure
Flow is fifteen gpm at the measured twenty-psi condition
Static pressure is necessarily twenty psi
The meter has unlimited capacity
Sections you finish are checked off in the contents.