head type & flow rate
spacing pattern
zone details
Perth sandy soils
Sandy soils absorb 12–25mm/hr. A PR above 20mm/hr risks runoff — cycle-and-soak is recommended.
Waterwise target
Water Corporation recommends 6–10mm per session for established lawns on sandy Perth soils.
MP Rotators
MP Rotators typically run 5–8mm/hr. Slow, but ideal for sloped or water-sensitive areas with minimal runoff risk.
Head-to-head spacing
Space heads so each throw reaches the adjacent head — typically 50–60% of diameter for uniform coverage.
How it works
What is precipitation rate?
Precipitation rate (PR) is the depth of water applied per hour in mm — the irrigation equivalent of rainfall intensity. A zone at 12mm/hr will apply 12mm in 60 minutes, or 6mm in 30 minutes.
How is PR calculated from spacing?
PR (mm/hr) = (flow per head in L/min × 60) ÷ area per head in m². For square patterns, area = spacing². For triangular patterns, area = 0.866 × spacing². Since 1 L/m² = 1mm, the result directly equals mm/hr.
What's a good precipitation rate for Perth?
For Perth's sandy soils, 8–18mm/hr is ideal. Above 20mm/hr may cause runoff on compacted or clay areas. Below 6mm/hr (typical of MP Rotators) means very long run times but minimal runoff risk.
Want to verify with a physical test?
Use our bucket test calculator to measure actual PR from catch can volumes — useful for confirming your calculated result against real field conditions.