Drip Irrigation
Part of Irrigation
Drip irrigation delivers water directly to the root zone of each plant through a network of pipes and small emitters, at a slow rate matched to the soil’s infiltration capacity. It is the most water-efficient irrigation method available, using 30–60% less water than surface flooding while producing equal or higher yields. A gravity-fed drip system requires no electricity and can be built from salvaged materials. For a rebuilding community, drip irrigation enables high-productivity vegetable gardens and orchards even where water is scarce.
How Drip Irrigation Works
A drip system has four components:
- Header tank: An elevated water source providing pressure by gravity. Minimum 0.5 m elevation; 1–2 m is ideal for most emitters.
- Main line: Pipe running from the tank to the field. Any watertight pipe or tube works — rubber hose, bamboo, clay pipe.
- Lateral lines: Smaller distribution pipes running along each crop row, connected to the main line.
- Emitters: Devices at each plant that restrict flow to a slow drip rate.
Water flows by gravity from the tank through the main line to the laterals. Emitters on the laterals deliver 1–8 liters per hour to each plant’s root zone.
Gravity-Fed System Design
Header Tank
The header tank provides pressure without a pump. Pressure = height. For most drip emitters, a head of 0.5–2.0 m of water (5–20 kPa) is sufficient. Greater height increases flow rate slightly.
| Tank Height | Pressure | Suitability |
|---|---|---|
| 0.5 m | ~5 kPa | Adequate for simple wicks and drip holes |
| 1.0 m | ~10 kPa | Good for most improvised emitters |
| 2.0 m | ~20 kPa | Adequate for commercial emitter types |
| 5.0+ m | ~50 kPa | Required for pressure-compensating emitters |
Tank volume should equal at least one full day’s water requirement for the system. For a 100-plant garden with 2 L/plant/day, a 200–300 L tank is the minimum.
Elevate the tank on a robust timber or stone platform. Instability is dangerous — a 200 L tank weighs 200 kg.
Main Line Sizing
| Lateral Lines Served | Recommended Main Line Diameter |
|---|---|
| 1–3 laterals | 20–25 mm internal diameter |
| 4–8 laterals | 32–40 mm internal diameter |
| 8–20 laterals | 50–63 mm internal diameter |
Bamboo culms (10–50 mm internal diameter) work well as main lines for small systems. Seal joints with clay or tree resin.
Lateral Line Layout
Run laterals along each crop row. Keep lateral length under 50 m where possible — longer runs cause unequal pressure and uneven water distribution across emitters.
| Crop | Lateral Spacing | Emitter Spacing | Emitter Flow Rate |
|---|---|---|---|
| Tomato, pepper, eggplant | 1.0–1.5 m between rows | 0.3–0.5 m (one per plant) | 2–4 L/hour |
| Squash, cucumber | 1.5–2.0 m between rows | 0.6–1.0 m | 3–6 L/hour |
| Lettuce, spinach, herbs | 0.3–0.5 m between rows | 0.2–0.3 m | 1–2 L/hour |
| Fruit trees | 3–6 m between trees | 2–4 emitters per tree | 4–8 L/hour each |
Emitter Types
Emitters restrict water flow to the desired rate. Several types can be built from available materials.
Drip Hole Emitter (Simplest)
Pierce the lateral pipe with a heated nail or pin. Hole diameter determines flow:
| Hole Diameter | Flow at 1 m Head | Flow at 2 m Head |
|---|---|---|
| 0.5 mm | 50–100 mL/hour | 70–140 mL/hour |
| 1.0 mm | 200–400 mL/hour | 280–560 mL/hour |
| 1.5 mm | 500–900 mL/hour | 700–1300 mL/hour |
For individual vegetable plants, a 0.8–1.0 mm hole is usually appropriate.
Hole Uniformity
Drip holes punched by hand vary in size, leading to unequal watering across a row. Check uniformity by running the system and collecting drip from several emitters over 5 minutes. If one drips twice as fast as another, the hole is too large — seal with wax or silicone and repunch.
Wick Emitter
Push a 10–15 cm length of braided cotton rope or folded cloth into a small hole in the lateral. The wick absorbs water and drips from its end. Flow is very slow (50–200 mL/hour) and self-regulating — as the soil wets, capillary pressure reduces drip rate automatically. Ideal for pots and small seedlings.
Bottle Emitter
Attach a small bottle or section of tube to the lateral using a rubber grommet or clay seal. Punch a small hole in the bottle bottom. The bottle fills and empties slowly, buffering flow variations. Useful where pressure is variable.
T-Connector Emitters
At each plant position, install a T-junction in the lateral pipe. From each T, run a short length of smaller-diameter tube (5–8 mm internal diameter, 20–30 cm long) ending in a drip hole or wick. This brings water directly to the base of each plant regardless of where the lateral runs.
Installation Procedure
Step 1: Site Survey
Measure the field dimensions, identify the water source, and determine the elevation available for the header tank. Map crop rows. Calculate the number of laterals, total lateral length, and number of emitters.
Step 2: Build and Fill the Tank
Construct the tank platform and install the tank. A simple gate valve or stopcock at the tank outlet controls flow. If no valve is available, use a removable plug — a tightly wrapped cloth bung works for short periods.
Step 3: Lay the Main Line
Run the main line from tank to field, burying it 5–10 cm deep where possible to protect it from sun degradation and physical damage. At each lateral connection point, install a T-junction or simply punch a hole and insert the lateral line tip, sealing around it with rubber, clay, or wrapped cloth.
Step 4: Lay Laterals
Roll out or lay laterals along each crop row. Secure them at plant level with small stakes or stones. Cap the far end of each lateral by pinching, tying a knot, or inserting a wooden peg.
Step 5: Install Emitters
Punch or insert emitters at each plant position. For established plants, position emitters 10–15 cm from the stem. For newly planted seedlings, place closer (5–8 cm).
Step 6: Flush and Test
Before connecting emitters, open the main line and flush all pipes for 1–2 minutes to clear debris. Then attach emitters and run the system for 30 minutes. Check that each emitter is dripping, that no laterals have burst, and that the tank empties at the expected rate.
Irrigation Scheduling
Run drip systems for a set number of hours each day based on crop water needs and emitter output.
| Season / Climate | Daily Water Need per Plant (Vegetable) | Run Time (at 2 L/hour emitter) |
|---|---|---|
| Cool, humid | 0.5–1.0 L | 15–30 minutes |
| Warm, dry | 1.5–3.0 L | 45–90 minutes |
| Hot, arid | 3.0–6.0 L | 90–180 minutes |
Observe the soil moisture at 10–15 cm depth every few days. If the soil is still wet at the next irrigation time, reduce run time. If it is dry and plants show any stress, increase run time or frequency.
Maintenance
| Task | Frequency | Notes |
|---|---|---|
| Flush main line and laterals | Weekly | Prevents sediment buildup in emitters |
| Check and unblock emitters | Weekly | Use a pin to clear clogged holes |
| Inspect for leaks | After each irrigation | Small leaks waste water and cause wet spots |
| Refill / replenish tank | Daily or as needed | Record consumption to track crop water use |
| Replace cracked laterals | As needed | Bamboo cracks with age; inspect monthly |
Filter at the Tank Outlet
The single most effective maintenance step is a simple filter at the tank outlet — a small piece of fine cloth or grass mat wedged into the outlet fitting. This catches sediment and organic debris before it reaches the emitters. Rinse the filter weekly.
Common Problems
| Problem | Cause | Fix |
|---|---|---|
| Emitter not dripping | Clogged; pressure too low | Unblock with pin; raise tank |
| Uneven wetness between plants | Inconsistent emitter holes; sloped laterals | Test each emitter; re-level |
| Lateral burst | Pressure too high; weak joint | Lower tank or reduce main line diameter |
| Water drips constantly even with valve closed | Valve/plug leaking | Replace or tighten |
| Roots grow into emitters | Common in buried systems | Raise emitters above soil surface |
Drip Irrigation Summary
Gravity-fed drip irrigation uses a header tank elevated 1–2 meters to supply water through a main line and laterals to individual plant emitters. Emitters — which can be as simple as punctured holes, wicks, or bottle attachments — deliver 1–6 liters per hour directly to the root zone. Main line diameter should be 20–50 mm depending on system size; laterals should not exceed 50 m length. Flush all pipes before connecting emitters. A filter at the tank outlet prevents clogging. Weekly maintenance (flushing, emitter checks, leak inspection) keeps the system reliable. Properly designed drip systems use 30–60% less water than surface irrigation while maintaining or improving yields.