Words used in this plan

Flow: how much water passes in a set time, in litres per hour (L/h) for a dripper, or cubic metres per hour (m³/h) for a pump or a pipe. One cubic metre is 1,000 litres.
Pressure: how hard the water pushes inside the pipe, measured in bar.
Head: pressure given as a height of water, in metres. One bar is about 10 metres of head.
Total head: the height the pump must lift the water, plus the pressure the system needs at the far end, plus what is lost to friction in the pipes, all in metres.
Zone: a part of the field watered at one time, through its own valve.
Head unit: the valves, filter and meter where the water enters the system. FAO calls it the control head; it has nothing to do with head as a height of water.
Main: the largest pipe, from the head unit to the zones. Sub-main: the smaller pipe along the end of the beds that feeds one zone's drip lines; FAO calls it a manifold.
Drip line: the pipe with drippers built in, laid along each bed.

Sources: FAO (2002), Irrigation Manual, Module 9: Localized irrigation: planning, design, operation and maintenance, units table, Figures 1 and 24, and troubleshooting table; FAO (2007), Handbook on Pressurized Irrigation Techniques, chapter 2: Pressure piped irrigation techniques.

The field, the beds and the drip line

The example is a flat field of 100 by 100 metres, one hectare, with a borehole at one side. It is split into four blocks of 50 by 50 metres, with beds 1.5 m apart, centre to centre, and one drip line along each bed, as in our crop guide.

The drip line is a 16 mm pressure-compensating line with a 1.0 L/h dripper every 0.30 m. Pressure-compensating means each dripper gives the same flow at the start of the line and at the far end, within its working range. The maker's sheet for this line (Netafim DripNet PC, 16150) gives a working range of 0.4 to 3.0 bar for the dripper, but this wall takes at most 2.2 bar, and it asks for filtering to 130 micron (120 mesh).

The same sheet allows lines of up to 175 m on flat ground with 1.0 bar at the inlet, so beds of 50 m are well within it. On a 2 percent uphill slope its limit falls to 140 m.

See the drip line in the store Water needs of tomato, pepper and onion

Source: Netafim (2024), DripNet PC AS TWD and MWD technical product sheet: dripper and dripline data, coils and run lengths.

Flow, zones and pumping hours

If the source cannot supply the whole field at once, the field is watered in zones, one after another. The sums below find how many zones the source can supply and how long it must pump.

Worked example, for illustration only

One hectare of tomato on drip, from a borehole

Assumptions

A flat field of 100 m by 100 m, split into four blocks of 50 m by 50 m.
Beds 1.5 m apart with one drip line each, 50 m long.
Drip line with 1.0 L/h drippers every 0.30 m, from the maker's sheet.
A borehole that gives 6 m³/h for as long as it is pumped. This is made up for the example; use your own pumping test.
Tomato at full growth needing 11.5 litres per metre of bed a day, and 6.0 litres in the first weeks, as worked in our crop guide: ETo of 6 mm a day, the low end of FAO's indicative 6 to 7 mm a day for a semi-arid area at a mean temperature of 15 to 25°C, FAO crop factors 1.15 and 0.6, beds 1.5 m apart, and drip getting about 90 percent of the water to the roots.

Working

Beds: 50 ÷ 1.5 = 33 beds in each block. Drip line: 4 blocks × 33 beds × 50 m = 6,600 m.
Each metre of drip line gives 1.0 ÷ 0.30 = 3.33 litres per hour, so the whole field at once would take 6,600 × 3.33 = 22,000 litres per hour, or 22 m³/h.
Zones: 22 ÷ 6 = 3.7, so the borehole needs at least 4 zones. One zone per block gives 4.
One zone: 33 × 50 = 1,650 m of drip line × 3.33 = 5,500 litres per hour, or 5.5 m³/h, within the borehole's 6 m³/h.
Run time at full growth: 11.5 ÷ 3.33 = 3.45 hours per zone, about 3 hours 30 minutes.
Pumping a day at full growth: 4 zones × 3.45 = 13.8 hours, about 14 hours.
Water a day at full growth: 6,600 m × 11.5 litres = 75,900 litres, about 76 m³.
In the first weeks: 6.0 ÷ 3.33 = 1.8 hours per zone, 7.2 hours of pumping, and 6,600 × 6.0 = 39,600 litres, about 40 m³ a day.
In hot weeks: FAO gives 8 to 9 mm a day for a semi-arid area above 25°C. At full growth that is 15.3 to 17.3 litres per metre of bed, so 4.6 to 5.2 hours per zone, 18.4 to 20.7 hours of pumping, and about 101 to 114 m³ a day.

Result: In this example four zones of 1,650 m of drip line match the borehole's 6 m³/h, and at full growth the pump runs about 14 hours a day in mild weather, about 7 in the first weeks, and 18 to 21 hours in hot weeks. Size the source and the power for the hottest month in which the crop is at full growth, and check that figure first: if the source cannot keep its flow for that long, or the power is not there for those hours, the plan needs a source that gives more water per hour, a smaller area, or a tank filled over more hours.

Sizing a storage tank Pumping hours for a solar pump Choosing a pump for your water source

Sources: Netafim (2024), DripNet PC AS TWD and MWD technical product sheet: dripper and dripline data, coils and run lengths; FAO (1986), Irrigation Water Management Training Manual No. 3: Irrigation Water Needs, chapter 3, Table 5; FAO (1998), Irrigation and Drainage Paper 56: Crop Evapotranspiration, chapter 6, Table 12; FAO (1989), Irrigation Water Management Training Manual No. 4: Irrigation Scheduling, Annex I, Table 8; FAO (2002), Irrigation Manual, Module 9: Localized irrigation: planning, design, operation and maintenance, units table, Figures 1 and 24, and troubleshooting table.

The layout

The main runs from the head unit to the middle of the field. At the edge of the field it meets the sub-mains of the two nearer zones, and in the middle those of the other two. Each sub-main runs along the end of its zone's beds, with a valve where it leaves the main, and the drip lines run from it along the beds. Only one zone valve is open at a time.

Water source and pump: here a borehole
Head unit: the filter, meter and valves where the water enters the system
Main pipe: buried, from the head unit to the middle of the field
Zone valves: one for each zone, and only one zone is watered at a time
Sub-main: runs along the end of the beds and feeds one zone's drip lines
Drip lines: one along each bed

Water from the borehole passes the head unit and runs along the main to four zones, each with its own valve, sub-main and drip lines along the beds.

Main, sub-mains and zone valves

Because one zone runs at a time, the main and each sub-main carry one zone's flow, 5.5 m³/h in the example, not the 22 m³/h of the whole field. That keeps the pipes smaller. Pipe makers advise keeping water in plastic pipes below 1.5 metres a second, FAO's handbook notes. Its table of the most a pipe should carry, worked at 1.7 metres a second as the upper limit, gives 9 m³/h for a 50 mm HDPE pipe (hard black polyethylene) and 15 m³/h for a 63 mm one. Friction over the length of the pipe decides the final size, so ask for it to be worked out, above all for a long main.

Main: if it is rigid PVC, it must always be buried, out of the sun. FAO gives at least 45 cm of cover for pipes up to 50 mm and 60 cm for pipes up to 100 mm.
Sub-mains: one for each zone, along the end of its beds, with a start connector for each drip line.
Zone valves: one at the start of each sub-main. A ball valve opens or closes with a quarter turn; automatic valves on a controller can switch the zones in turn.
Pressure: the drip line in the example takes at most 2.2 bar. If the pressure at a zone can be higher, a pressure regulator at the start of the sub-main keeps it in range; that is where FAO's handbook places them.
Flushing: the far end of each sub-main and of each drip line must open, so dirt can be flushed out, one line at a time, until the water runs clean.

Choosing pipes, valves and pressure regulators See a hand valve for a zone in the store See valves and automation

Sources: FAO (2007), Handbook on Pressurized Irrigation Techniques, chapter 3: Irrigation equipment and jointing techniques, Tables 3.1 and 3.4; FAO (2007), Handbook on Pressurized Irrigation Techniques, chapter 2: Pressure piped irrigation techniques; Netafim (2024), DripNet PC AS TWD and MWD technical product sheet: dripper and dripline data, coils and run lengths; FAO (2002), Irrigation Manual, Module 9: Localized irrigation: planning, design, operation and maintenance, units table, Figures 1 and 24, and troubleshooting table.

What the head unit holds

The head unit is where the water is cleaned, measured and checked before it enters the field. FAO's handbook and irrigation manual list these parts:

A non-return valve straight after the pump, so water cannot run back when the pump stops.
An air valve, to let trapped air out of the pipe.
If the water carries sand, a sand separator (hydrocyclone) at the start of the unit. The drip line's maker asks for one wherever the water holds more than 2 parts per million of sand.
If you will feed fertiliser through the drip, two outlets to connect a fertiliser injector, with a shut-off valve between them.
The filter, with a pressure gauge on each side. If the pressure before the filter is right but the pressure after it is low, the filter needs cleaning.
A water meter, which records how much water has passed, and isolation valves, so each part can be shut off for cleaning or repair.

Choosing a filter for drip irrigation Feeding fertiliser through drip See filtration and fertigation

Sources: FAO (2007), Handbook on Pressurized Irrigation Techniques, chapter 2: Pressure piped irrigation techniques; FAO (2007), Handbook on Pressurized Irrigation Techniques, chapter 3: Irrigation equipment and jointing techniques, Tables 3.1 and 3.4; FAO (2002), Irrigation Manual, Module 9: Localized irrigation: planning, design, operation and maintenance, units table, Figures 1 and 24, and troubleshooting table; Netafim (2024), DripNet PC AS TWD and MWD technical product sheet: dripper and dripline data, coils and run lengths.

Parts list for the example

Every quantity below follows from the assumptions above. Change the field, the beds or the source and the numbers change with them.

Part	Quantity in the example	Where the number comes from
Drip line, 16 mm, 1.0 L/h every 0.30 m	6,600 m: 7 rolls of 1,000 m	132 beds of 50 m, with 400 m left over for repairs
Start connectors	132	One where each drip line joins its sub-main
Drip line ends that open for flushing	132	One at the far end of each drip line
Sub-main pipe	200 m	4 zones × 50 m along the end of the beds
Sub-main flush ends	4	One at the far end of each sub-main
Zone valves	4	One for each zone
Main pipe	50 m, plus the distance from the borehole to the field	From the edge of the field to its middle
Joints where the main meets the sub-mains	2	A cross at the edge of the field and a tee in the middle
Head unit	1	Non-return valve, air valve, filter with two gauges, water meter and isolation valves, plus a sand separator and injector outlets if needed
Pressure regulators	Up to 4, only if needed	One at the start of each sub-main where the pressure could pass 2.2 bar
Pump	1	Chosen for one zone's 5.5 m³/h at the total head of your site

Bends, reducers, trench work and the pump's power supply depend on the site and are not counted here. Ask for them on the quote, and compare quotes on the same quantities.

Comparing irrigation quotes

Sources: Netafim (2024), DripNet PC AS TWD and MWD technical product sheet: dripper and dripline data, coils and run lengths; FAO (2007), Handbook on Pressurized Irrigation Techniques, chapter 2: Pressure piped irrigation techniques; FAO (2007), Handbook on Pressurized Irrigation Techniques, chapter 3: Irrigation equipment and jointing techniques, Tables 3.1 and 3.4.

Check before you order

Measure the field and how much it slopes. On a slope, run the beds and drip lines along the contour, and check the run length: this line's limit falls from 175 m on flat ground to 140 m on a 2 percent uphill slope.
Test the source: how much water it gives an hour, for how many hours, and in the driest month.
Have the water tested for sand and dirt, to choose the filter and to know whether you need a sand separator.
Measure the distance and the rise from the source to the field: both add to the pipe and to the total head.
Match the drippers to your soil: on sandy soil water spreads less to the sides, and FAO says drippers with a higher flow are needed to wet the soil across the bed.
Count the hours of power the pump will have each day, and compare them with the pumping hours at full growth.

Is your site ready for irrigation?Watering sandy, loamy and clay soils

Sources: FAO (1988), Irrigation Water Management Training Manual No. 5: Irrigation Methods, chapter 6; Netafim (2024), DripNet PC AS TWD and MWD technical product sheet: dripper and dripline data, coils and run lengths; FAO (2007), Handbook on Pressurized Irrigation Techniques, chapter 2: Pressure piped irrigation techniques.

Trademarks belong to their owners. ASFA IRRIGATION NG LIMITED is an independent company; no partnership is implied.

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Planning drip irrigation for a one-hectare vegetable farm.