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Irrigation audit — measure it before you replace it

An audit puts numbers on how evenly your system actually waters. It is the cheapest way to find out whether you need a new system, a few adjustments, or just a better schedule.

In short

What is irrigation audit?

An irrigation audit measures how much water each part of your landscape actually receives, rather than how much the controller says it applied. The core test is simple and physical: catch cans are laid out across a zone, the zone runs for a set time, and the volume in each can is compared. Wide variation between cans means the whole zone must be over-run to keep its driest spot alive — which is where most residential water waste comes from.

The job

How irrigation audit actually works

  1. Site walk-through and inventory

    The auditor records what is actually installed: zone count, head types and nozzles per zone, controller model, sensors, and the plant material each zone serves. On older systems this frequently differs from any drawing that exists.

    Watch for: Mixed head types found on one zone. It is extremely common on systems that have been repaired over many years, and it means that zone can never water evenly no matter what schedule you set.

  2. Pressure readings at the heads

    Pressure is measured at the nozzle, not at the valve — including at the furthest head on each zone. Pressure above design causes misting; below design causes short throw and dry gaps.

    Watch for: Pressure taken only at the hose bib. That number tells you about your supply, not about what the last head on a long lateral is experiencing.

  3. The catch-can test

    Identical containers are placed in a grid across a zone, the zone runs, and the volume in each is measured. The results give both an application rate — how fast the zone applies water — and a uniformity figure describing how evenly it lands.

    Watch for: Too few cans, or cans placed only in the middle of the zone. Uniformity problems live at the edges and between heads; a grid that avoids those places produces a flattering and useless result.

  4. Interpret uniformity against what it costs you

    Poor uniformity has a specific financial consequence: to keep the driest area acceptable, the whole zone must run long enough for that spot, and everywhere else is overwatered by the difference. Improving uniformity reduces the run time the zone needs.

    Watch for: A uniformity number quoted without a recommendation attached. The figure is only useful if it comes with what to change and what that change would achieve.

  5. Check soil and infiltration

    How fast the soil can absorb water determines whether a zone should run once or in several shorter cycles. Clay and compacted soil accept water far more slowly than the rate most spray zones apply it, which produces runoff long before the root zone is wet.

    Watch for: A recommendation to increase run times on clay soil without cycle-and-soak. Longer single runs on slow soil produce more runoff, not more moisture.

  6. Build a schedule from the measured numbers

    With an application rate per zone and local seasonal demand, run times stop being guesses. Each zone gets a time derived from what it measurably applies and what its plants measurably need.

    Watch for: A schedule handed over as a single sheet with no explanation of how to change it later. You need to understand the logic, because next season's weather will not match this one's.

  7. Prioritised recommendations, cheapest first

    A good audit report is ordered by return: schedule changes first because they are free, then nozzle and arc corrections, then pressure regulation, then zone splits, then equipment. Replacement should be at the bottom, if it appears at all.

    Watch for: A report whose first recommendation is a new system from the company that wrote the report. That is a sales visit with catch cans.

Money

What does irrigation audit cost?

An audit is usually a flat diagnostic fee scaled by zone count and property size — a fraction of what a system replacement costs. Some water utilities offer subsidised or free audits; it is worth asking yours. Full ranges in the Cost Guide.

See the full irrigation audit cost guide — by material, size and region →

Straight answer

When irrigation audit is the wrong call

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Types of irrigation audit

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FAQ

Irrigation Audit — questions people ask

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Distribution uniformity describes how evenly water lands across a zone. It matters because you are forced to schedule for the driest spot — if one corner receives half what the rest does, you must run the whole zone twice as long to keep that corner alive, and everything else gets double what it needed. Improving uniformity lets you cut run times without anything going brown.
Often, yes, and it is worth saying plainly because nobody selling installations will. Most residential inefficiency comes from schedules, pressure and nozzle mismatch — all correctable on existing pipework. A new system corrects those things too, at many times the price, and a new system that is badly zoned reproduces the problem. Replacement is genuinely warranted when the pipe is failing or the zoning cannot be salvaged, not merely when the system is old.
Typically a few hours on a residential property, because the catch-can test has to be laid out, run and measured zone by zone and that cannot be rushed. Larger properties run to a full day or more. If someone offers to audit a multi-zone system in half an hour, they are inspecting it, not measuring it.
The common findings repeat across most systems: run times set by habit rather than by application rate, pressure above the design range causing misting, mismatched nozzles within a zone, arcs throwing onto hard surfaces, and beds still being served by spray heads that would be better on drip. The first two cost nothing or very little to fix, which is why a good report puts them at the top.
Frequently more worth it, not less. A weather-based controller calculates run times from an assumed application rate for each zone — and if you guessed that number during setup, every clever adjustment it makes is built on a wrong figure. An audit gives it the measured rate to work from, which is the difference between a smart controller that saves water and one that automates an existing error.
Some do, either directly or through a subsidised programme, particularly in regions with sustained water stress. Availability, eligibility and what the audit covers vary entirely by utility and can change from year to year, so there is no general answer — check your own provider's website or call them before paying for a private audit.

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