How to Calculate Your Water Application (mm/h) Based on L/h Flow Rate
When you install a dripline system, one of the most important performance indicators to understand is your water application rate — the amount of water your system applies to the soil, usually expressed in millimetres per hour (mm/h). This tells you how deep your irrigation water penetrates the soil and helps you match irrigation time to crop water requirements.
Understanding the Terms
- L/h (litres per hour): The amount of water each emitter releases every hour.
- Emitter spacing (cm): The distance between emitters along the dripline.
- Row spacing (cm): The distance between two dripline rows in your field.
- mm/h (millimetres per hour): The depth of water applied to your soil surface per hour of irrigation.
The Formula
To calculate your water application rate in mm/h, use the following simple formula:
Where:
- Emitter Flow Rate is in litres per hour (L/h)
- Emitter Spacing and Row Spacing are in centimetres (cm)
Example Calculation
Let’s say you’re using 1.6 L/h emitters spaced 30 cm apart, with your dripline rows also spaced 30 cm apart. Your application rate would be:
This means your dripline applies approximately 0.18 mm of water per hour per square centimetre. If you wanted to apply 5 mm of irrigation water, you’d need to irrigate for roughly 28 hours (5 ÷ 0.18).
Typical Application Rates
For reference, here’s a general idea of what’s typical across common systems:
- Low-flow systems (0.8–1.0 L/h): 0.10–0.15 mm/h.
- Medium-flow systems (1.3–1.6 L/h): 0.16–0.20 mm/h.
- High-flow systems (2.0–3.8 L/h): 0.25–0.35 mm/h.
Keep in mind that this is only a baseline — your exact values will depend on emitter spacing, row layout, and soil type.
How to Use This Information
- Use the calculation to determine how long to irrigate to meet your crop’s daily water needs.
- Compare application rates between systems before installation.
- Adjust flow rate or spacing to reduce runoff or overwatering.
Where to Find Dripline Irrigation in South Africa
Our Afriq Drip range is proudly manufactured in South Africa, offering reliable, value-for-money irrigation solutions for farms of all sizes.
You can find our dripline rolls and fittings at most agricultural Co-Ops and irrigation suppliers across the country. Stock availability may vary, as we manufacture to order, so please allow 2–3 weeks lead time.
Prefer to buy online? Visit:
www.irrigationonlinesa.co.za
Or contact our distributor to find your nearest retailer:
www.iunlimited.co.za/contact/
