Drip Irrigation Setup and Maintenance for Small Farms

A drip system is not complicated, but it is unforgiving of omissions. Leave out filtration and it blocks. Leave out pressure control and the far end of the row gets a fraction of what the near end gets. Leave out a flush valve and sediment collects at the dead ends until the last emitters stop.

This page covers the ways of applying water, what each part of a drip system does, how to calculate flow rate and run time from your own numbers rather than copying someone else's, and the maintenance that decides whether the system still works in its third season. Equipment is described by function, not by brand.

Ways of applying water

By hand. Simple, no equipment, and it gives you daily contact with every plant — which for a new grower is genuinely valuable, because you learn what the medium feels like. The limits are uniformity and labour: two people watering the same block will not apply the same amount, and neither will the same person on a busy day.

Drip (localized irrigation). Water is delivered slowly at each plant. FAO notes that drip typically wets only around 30 percent of the root zone volume, which is the point — water goes where roots are rather than over the whole surface. It suits row crops and containers, gives high uniformity when designed properly, and keeps foliage dry, which matters for disease in humid conditions.

Sprinkler and micro-sprinkler. Covers area rather than points. Useful for establishing seedlings and for cooling. The drawback in a humid climate is wet foliage and prolonged leaf wetness. It also concentrates two water quality problems: FAO 29 tightens both sodium and chloride limits to 3 meq/L for sprinkler irrigation compared with surface application, and notes that water with soluble calcium, bicarbonate and sulphate leaves white deposits on leaves and fruit when sprinklers are used.

Recirculating systems. Solution is collected and re-used. Saves water and fertiliser, but everything dissolved that the plants do not take up accumulates, so the solution must be monitored and eventually discharged — and one root disease can move through the whole system.

Parts of a drip system

Working from the water source outward, as set out in FAO's irrigation training material:

  • Pump unit — takes water from the source and provides the pressure the system needs.
  • Control head — valves controlling discharge and pressure for the whole system, usually housing the filters and any fertiliser injection.
  • Filtration — the component that decides whether the system survives. See the next section.
  • Pressure regulation — holds the system at its design pressure. Without it, excessive pressure dislodges emitters and ruptures drip tape.
  • Mainline and submains — carry water to the field. PVC or polyethylene.
  • Laterals — the lines running along each row, typically 13 to 32 mm diameter.
  • Emitters — control the discharge from lateral to plant.
  • Flush valves at the end of each lateral — without them there is no way to clear the sediment that collects at the dead end.
  • Timer or controller — makes the schedule repeatable. Optional, but the alternative is that the schedule depends on who is on the farm that day.

The single fact that explains why filtration is not optional: emitter waterways are 0.2 to 2.0 mm in diameter. Orifice-type emitters have flow areas of 0.2 to 0.35 mm², long-path types 1 to 4.5 mm². Particles that pass through any ordinary pipe will bridge and block these.

Filtration

Two questions: how fine, and what type.

How fine. Agriculture Victoria states that the smallest pathway through most emitters is 500 to 1,000 microns, and that drip systems therefore generally require at least 120 mesh, which is 130 microns. An emitter manufacturer's own product sheet specifies the same: 130 micron, 120 mesh. Clemson Cooperative Extension advises 150 mesh regardless of type, with some emitters needing 200 mesh. Virginia Cooperative Extension notes that a 200-mesh screen with an opening of 0.003 inches removes particles the size of fine sand, suiting most groundwater systems.

The sizing rule. Filter to remove particles larger than roughly one-tenth of the smallest opening in the emitter flow path — stated in those terms by both Virginia Cooperative Extension and UF/IFAS. Agriculture Victoria gives a slightly wider window, one-sixth to one-tenth for drip. A Philippine national standard gives one-tenth to one-quarter. You will sometimes see "one-seventh" quoted; we could not find any source for that figure and would not rely on it.

Which type, by water source:

Filter type Suited to Filtration range
Screen Groundwater and clean-to-average water; sediment 60 – 200 mesh
Disc Mixed organic and inorganic load including algae; backflushes with less water than media 40 – 600 mesh (400 – 25 microns)
Media / sand Surface water, open reservoirs, ponds, canals, algae Bed of 1.5 – 3.5 mm gravel or sand
Hydrocyclone / sand separator Well or river water carrying sand and silt — fitted ahead of a screen filter Centrifugal separation

This maps onto the Thai water sources discussed on our water quality page: a borewell carrying fine sand wants a hydrocyclone ahead of a screen; canal or pond water wants media or disc filtration because the load is organic; treated municipal supply generally needs only a screen.

When to clean. Judge by pressure difference across the filter, not by appearance. Agriculture Victoria gives clean-filter head loss as 5 to 20 kPa for screen, 20 to 50 kPa for disc and 30 to 70 kPa for media, and advises backflushing before reaching 50, 70 and 100 kPa respectively. Fitting pressure gauges either side of the filter is what turns this from guesswork into a reading.

Working out flow rate and run time

These are the formulas. Put your own numbers in rather than copying a schedule, because the answer depends on your crop, your canopy, your emitters and your season.

Step 1 — crop water requirement. From FAO 56:

ETc = Kc × ETo

where ETo is reference evapotranspiration for your location and season, and Kc is the crop coefficient for your crop and growth stage. Published ETo figures for Thailand, by station and month, are on our main water and irrigation page.

Step 2 — adjust for the fact that drip wets only part of the ground. This reduction factor is not in FAO 56; it is in FAO's Irrigation Manual, Module 9:

IRn = (ETc × Kr) − R + LR
IRg = IRn / Ea

where IRn is net irrigation requirement, Kr is the localization factor based on percentage ground cover, R is effective rainfall, LR is the leaching requirement, Ea is field application efficiency and IRg is the gross requirement.

A caution about Kr: FAO Module 9 prints three published versions of it, and they disagree. At 50 percent ground cover they give 0.59, 0.75 and 0.60 respectively. Treat Kr as an approximation, not a precise figure. A simpler closed form used in the Philippine standard is Kr = 0.1 × the square root of percentage ground cover, which returns 0.71 at 50 percent cover and 1.0 at full cover.

Step 3 — run time. From FAO Module 9:

Ta = IRg / (Np × q)

where Ta is daily operating time in hours, Np is the number of emitters per plant and q is emitter discharge in litres per hour. In plain words: the volume each plant needs, divided by the rate at which its emitters deliver.

Typical values to sanity-check your answer. FAO Module 9 gives operating pressures of 10 to 20 metres head, roughly 1.0 to 2.0 bar, and emitter flow rates of 2 to 8 L/h. Another FAO handbook gives drippers operating at approximately 1.0 bar with flow rates from 1.0 to 24 L/h; FAO's training manual gives 2 to 20 L/h and application every one to three days. Drip tape runs lower, around 0.7 bar. If your calculated run time comes out at eight hours or at four minutes, check your inputs.

How far one emitter wets, from FAO Module 9: sandy soil 0.5 to 2 m², loam 2 to 6 m², clay 6 to 15 m². This is why emitter spacing has to follow soil texture — spacing that gives a continuous wetted strip in clay will leave dry gaps between plants in sand.

Pressure and pressure compensation

Emitter discharge varies with pressure according to:

q = k × Hx

where q is discharge, H is pressure head at the emitter, k is a discharge coefficient and x is the emitter's discharge exponent. The exponent is what matters. UF/IFAS explains that values of x range from 0 to 1, with around 0.5 common for turbulent-flow emitters; low values indicate emitters relatively insensitive to pressure change, and high values emitters whose flow changes a lot with pressure.

Emitter type Exponent x
Laminar flow / capillary 1.0
Microtube about 0.85
Long or spiral path 0.65 – 0.8
Tortuous path 0.5 – 0.7
Turbulent flow / orifice 0.5
Vortex about 0.4
Pressure-compensating about 0

A pressure-compensating emitter uses a flexible orifice that changes diameter with pressure, holding flow steady across a range. One manufacturer's specification gives a compensating range of 1.0 to 4.0 bar, holding flow within a stated tolerance; other designs regulate from lower pressures, so treat that as one example rather than a universal figure.

When compensation is necessary: whenever elevation differences or friction losses along the laterals would otherwise push flow variation past the design standard. Concretely, that means sloping ground — every 10 metres of elevation change is about 1 bar of head — and long laterals, where accumulated friction starves the far end. Manufacturers publish separate maximum lateral length tables for uphill, flat and downhill runs, which is direct evidence that slope governs the decision.

Checking the system actually works

A system can be installed correctly and still deliver badly. Uniformity is the measure, and it is worth checking rather than assuming.

Field emission uniformity is measured by catching output from a sample of emitters across the block for a timed period:

EU = 100 × (average discharge of the lowest one-quarter of emitters) / (average discharge of all emitters measured)

Acceptable values, from ASABE's design reference: a minimum design emission uniformity of 80 percent, and 90 percent where fertiliser is injected through the system. FAO Module 9 recommends 90 to 95 percent for point-source emitters on widely spaced perennials, and 70 to 85 percent for line-source emitters on undulating terrain. UF/IFAS classifies above 90 percent as excellent, 80 to 90 good, 70 to 80 fair, 60 to 70 poor and below 60 unacceptable.

The related Christiansen uniformity coefficient, defined in 1942 and still the standard for sprinkler systems, is 100 × (1 − mean absolute deviation / mean application depth).

A falling uniformity reading over seasons is the earliest warning of clogging — usually visible in the numbers well before anyone notices a dry plant.

Maintenance — clogging, biofilm and flushing

Clogging comes in three kinds, and they need different treatments: physical (sediment, sand from wells, particulates from canals and ponds), chemical (carbonate scale, iron and manganese precipitation) and biological (algae, bacterial slime, organic deposits).

A clogging hazard table widely reproduced in extension literature, originally from Nakayama and Bucks (1986), rates the risk:

Factor Slight Moderate Severe
Suspended solids (ppm) below 50 50 – 100 above 100
Dissolved solids (ppm) below 500 500 – 2000 above 2000
pH below 7.0 7.0 – 8.0 above 8.0
Iron (ppm) below 0.1 0.1 – 1.5 above 1.5
Manganese (ppm) below 0.1 0.1 – 1.5 above 1.5
Hardness as CaCO3 (ppm) below 150 150 – 300 above 300
Bacteria (per mL) below 10,000 10,000 – 50,000 above 50,000

Note that a farm on canal or pond water starts in the moderate-to-severe column on suspended solids and bacteria, and a farm on hard borewell water starts there on hardness and pH. Water source determines maintenance burden.

Flushing. The most important routine task, and the cheapest. Open the ends of the laterals and let water run until it comes out clean. Virginia Cooperative Extension advises continuing for at least two minutes of clean water; UF/IFAS notes it normally takes only a minute or two and recommends flushing at least once a month during the season, and every four to six weeks when the system is idle. Agriculture Victoria advises three times a season on clean water and at least once every fourth irrigation on dirty water.

The velocity needed. ASABE Engineering Practice EP-405 specifies a minimum flushing velocity of 0.3 m/s, corroborated by two extension publications quoting 1 foot per second. A study that specifically tested velocities from 0.16 to 0.62 m/s concluded that the 0.3 m/s figure still appears adequate for most microirrigation systems under typical conditions. You will also see 0.5 m/s quoted; we found it in one guidance document with no citation given, so treat 0.3 m/s as the standard and 0.5 m/s as a margin.

Chlorination for biological clogging. Published rates differ, so here is the range rather than a single number. Virginia Cooperative Extension: 1 to 2 ppm free chlorine measured at the end of the lateral furthest from the injection point, with 10 to 30 ppm for shock treatment, and a semi-annual shock likely sufficient for groundwater systems. A treatment manual hosted by Virginia Tech: continuous 1 to 2 ppm during irrigation or in the last hour of each cycle; chlorine must contact algae and bacteria for at least 30 minutes, so hold 1 to 2 ppm free residual for 60 minutes; end-of-season 5 to 20 ppm; shock above 50 ppm left in the system for 24 hours before flushing. Agriculture Victoria: run the pump 10 to 15 minutes after injection, then shut the system down for 2 to 24 hours.

The detail most guides omit, and it matters a great deal on Thai borewell water: chlorine only works as hypochlorous acid, and how much of your dose exists in that form depends on pH. At pH 8 only about 22 percent is in the active form; at pH 7, 73 percent; at pH 6, about 96 percent. Chlorinating hard alkaline water at pH 8 delivers roughly a quarter of the effect of the same dose at pH 6. If your water is alkaline, correct pH first or the treatment is largely wasted.

Safety, stated as the source states it: active chlorine solutions are dangerous to people and animals; contact with skin can cause serious burns, contact with eyes can cause blindness, and swallowing may be fatal. Never mix chlorine with acid.

Acid treatment for scale. Preventive injection targets pH just below 7.0 to stop calcium carbonate precipitating. Removing scale that has already formed needs a lower pH: Agriculture Victoria gives pH 2 to 4 depending on the deposit, and Virginia Cooperative Extension mentions as low as pH 2. Flush thoroughly afterwards. Acid and chlorine are injected on separate occasions, never together.

Harvesting rainwater in the wet season

In a monsoon climate, storing rain is often a cheaper answer to a salinity problem than treating salty water. The arithmetic is simple:

S = R × A × Cr

where S is the annual supply in cubic metres, R is annual rainfall in metres, A is catchment area in square metres and Cr is the runoff coefficient.

Runoff coefficients — two independent sources agree closely. A field handbook gives galvanised iron sheet above 0.9, aluminium sheet 0.8 to 0.9, glazed tiles 0.6 to 0.9, flat cement roof 0.6 to 0.7 and thatch 0.2. A peer-reviewed measurement study found sloping clay tile, metal sheet and polycarbonate all above 0.90, and a flat gravel roof 0.62, concluding that sloping smooth roofs harvest up to about 50 percent more than flat rough ones.

To make that concrete: a 200 m² metal roof in a region receiving 1,470 mm annually — the mean for the Northeast across 27 stations over 30 years — yields roughly 265 m³ a year at a coefficient of 0.9. That calculation is ours, using the formula and figures above.

Sizing the storage. The demand-side method: daily demand multiplied by the length of the dry period you must bridge. The supply-demand method plots cumulative runoff against cumulative use, with required storage being the largest gap between the two lines. For a greenhouse crop, Wageningen suggests storage of about 1,500 m³ per hectare, covering 20 to 90 percent of a tomato crop's water need depending on rainfall pattern and storage.

Gutter sizing, from the same field handbook: at least 1 cm² of gutter cross-section for every 1 m² of roof. Place the outlet at least 15 cm above the tank floor so sediment stays put.

First flush. Divert the first rain that washes dust and droppings off the roof. Thailand's Department of Health advises letting the first rain wash the roof and gutters and discarding it, after sweeping both thoroughly. For a volume, the Texas rainwater manual offers a rule of thumb of at least 10 gallons per 1,000 square feet of catchment, with recommendations ranging to 49 gallons — about 0.4 to 2.0 litres per square metre, a conversion we have made. It labels this a rule of thumb, and we found no research-derived figure.

Biological risk is real and should not be glossed over. A global review of roof-harvested rainwater tanks found E. coli in 24 to 92 percent of samples across studies, with every study reviewed having at least one tank exceeding WHO drinking water guidelines. In the Thai survey cited on our water quality page, total coliform was found in around 87 percent of rainwater samples. For irrigating crops eaten raw, that argues for more caution than rainwater's clean chemistry suggests.

Practical measures, from the same sources: mesh over tank openings to exclude animals and insects; sand filtration at the inlet; chlorination where treatment is warranted, at initial rates of about 7 g calcium hypochlorite or 40 mL sodium hypochlorite per 1,000 litres and weekly maintenance of about 1 g or 4 mL per 1,000 litres, targeting 0.2 to 0.5 mg/L residual. Thailand's Department of Health additionally advises fitting plastic mesh over the container mouth before the lid, and notes airborne particulates and combustion gases as hazards near factories or heavy traffic.

For irrigation specifically, sediment filtration before the emitters matters more than disinfection — which returns you to the filtration section above.

Downloads

Thai and English editions are being prepared.

Related guides

Sources

  • FAO. Irrigation Water Management: Irrigation Methods, Training Manual 5, Ch. 6. fao.org
  • FAO. Irrigation Manual Module 9 — Localized irrigation (Savva & Frenken, eds.). fao.org
  • Phocaides, A. (2007). Handbook on Pressurized Irrigation Techniques, 2nd ed., FAO. fao.org
  • Allen, R.G. et al. (1998). Crop evapotranspiration, FAO Irrigation and Drainage Paper 56, Ch. 6. fao.org
  • Ayers, R.S. & Westcot, D.W. (1985). FAO Irrigation and Drainage Paper 29 Rev. 1. fao.org
  • Agriculture Victoria. Filtration for drip irrigation and Drip system maintenance and monitoring. agriculture.vic.gov.au
  • Shortridge, J. & Benham, B. (2023). Filtration, Treatment, and Maintenance Considerations for Micro-Irrigation Systems, Virginia Cooperative Extension 442-757. vt.edu
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  • Evans, Wu & Smajstrala. Microirrigation Systems, Ch. 17 in Design and Operation of Farm Irrigation Systems, ASABE.
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  • Texas Water Development Board (2005). The Texas Manual on Rainwater Harvesting, 3rd ed. twdb.texas.gov
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