Caltech Drip Irrigation Project in Pasajquim Village, Guatemala - July 2 to 8, 2008
Summary: Drip irrigation systems were installed in two 1,500 meter2 community gardens, one fed
from the village water reservoir, the other from stored reservoir overflow. Despite multiple difficulties,
both systems were successfully installed. Students learned hands-on technical project execution as
specification, schedule, cost, materials, and expeditious redesign were balanced against each other in
an environment with many simultaneous constraints. Students worked with villagers far different from
themselves, receiving embraces and tearful kisses of gratitude for what they had accomplished.
System Design: Both systems included master shut-off valves, particle filters, and air vents. Filtered
water was distributed by PVC pipe to 5 branch subsystems, each containing a shutoff valve, a 10 psi
pressure regulator, and a 4 m run of recycled rubber tubing that had 6 or 8 connections to 30 or 50 m
runs of “t-tape” drip irrigation tubing.
Garden A was relatively level (3 m internal elevation variance), fed from the village water reservoir
that was about 400 m distant, and used 1” PVC pipe for internal distribution.
Garden B was sloped (7 m internal elevation variance) and gravity fed from a 750 liter storage tank 70
m distant that provided 12 psi static pressure. Because of this low input pressure, 2” PVC was used
for internal distribution to reduce pressure loss. The village reservoir is constantly fed by a distant
spring. From about 10 PM until 7 AM, when there is minimal village water usage, the reservoir
overflows into a drain pipe. A bypass valve and tees were inserted into this drain pipe that routed the
overflow into the 750 liter storage tank and then back into the drain pipe after the storage tank filled.
Project Specification: Unlike Caltech initiated projects, this project was requested by Fundación
Solar, a Guatemalan NGO, and adopted by the Caltech Y as a community service project. The
system was designed without knowing the reservoir overflow rate, daily watering needs, or storage
tank fitting sizes. Both gardens enlarged beyond what existed when a site survey was performed.
Material Availability: Most parts were brought from the USA by the project team but additional parts
were needed to adapt undefined fitting sizes and replenish spare parts consumed by the garden
enlargements and poor workmanship. The closest hardware store, 30 minutes away, had very limited
inventory. Parts ordered by cell phone and delivered by mini-bus were often late, incorrect,
unavailable, or required multiple parts to replicate an unavailable part.
Constrained Schedule: Only 4½ working days were available to install and test the systems and
then train the gardeners in operation and maintenance. The schedule was exacerbated by daily rains
that limited working hours. Because installation was during the rainy season, it was impossible to
verify system functionality during the dry season when they will be needed.
Untrained Installers: The project team members had never previously installed a drip irrigation
system or an overflow fed storage tank. Volunteers from other project teams were unfamiliar with
installation processes and workmanship requirements and some work needed rework and repair.
Language and Cultural Difficulties: Gardener training was done in elementary Spanish by project
staff and translated into Quiché. The system is low-tech by US standards but it is probably the most
complex system the gardeners have ever operated and maintained. Ongoing local support will be
provided by a Universidad Landívar student who lives several hours away from the village.
System Testing Results and Ongoing Concerns:
Overflow Capacity: During initial testing, the new overflow and storage tank system using 2” PVC
pipe was unable to accommodate the overflow from the pre-existing 3” PVC pipe and the reservoir
overflowed, flooding an access road. An improvised storage tank fitting that constricted overflow down
to a 1” aperture was replaced and the overflow was accommodated without replacing the 2” PVC with
3” PVC. It is assumed, but uncertain, that the observed rainy season overflow was worst case.
Tank Capacity: the pre-existing watering flow rate and duration indicated daily usage of about 900
liters, 20% greater than the storage tank capacity. This can be accommodated by watering before 7
AM when overflow can still replenish the storage tank. The reservoir reportedly overflows even during
the dry season when the irrigation system is actually needed but this could not be verified.
Excessive Pressure Drop: The drip tubing specified flow rate of 5 liters/hour/meter with 900 meters
of tubing operating yields a theoretical flow rate of 4500 liters/hour or 75 liters/min. This correlates
reasonably well with an observed flow rate of 70 liters/min. However, this flow rate caused a
significant pressure drop in the more than 400 m of pipe from the reservoir to garden A. It was
impossible to generate sufficient pressure to irrigate the entire garden simultaneously so this garden
must be irrigated in 2 or 3 sections. This was not deemed to be a significant constraint but future
installations should use lower flow (1/2 as much) drip tubing that will not incur such a large pressure
drop. A Guatemalan distributor donated the high flow tubing and had no low flow tubing available.
Buried Drip Tubing: If the tubing is not buried it irrigates less efficiently due to surface evaporation
and is subject to sunlight degradation that reduces its life. T-tape deflates when unpressurized and
reinflates when repressurized. Initially, buried t-tape was reportedly unable to reinflate but further
careful testing indicated that reinflation did indeed occur. All t-tape was left unburied and the
gardeners were instructed to experiment with buried tape, possibly using mulch rather than dirt.
Fitting Leakage: The recycled rubber tubing was fairly rigid and difficult to uniformly puncture for
insertion of drip tubing adapter fittings. Leakage around these fittings was not significant but future
installations should use softer tubing and a more controlled puncturing process.
Maintenance: Although all gardeners were instructed in system operation, filter cleaning, and t-tape
repair, there is some concern that they will be able to maintain the system with very limited external
support. There were remnants in the village of high tech systems such as on-demand water heaters
that had malfunctioned and were then abandoned rather than repaired.
Cost/Benefit Analysis: The parts list costs were about $300 for Garden A, $400 for Garden B
(including cost of donated drip tubing) and $400 for the overflow storage tank system. Actual
expenditures were about 40% higher due to rework, scrap, spare parts, unused parts, and parts
fabricated to replace unavailable parts. Donated installation labor cost has not been estimated. Each
system will reduce watering labor by more than 2 hours per day and may increase dry season crop
yields. This benefit cannot be estimated without future crop yield data, which will probably be
anecdotal and unreliable. It is possible that pesticide usage would increase crop yields even more
than irrigation improvements.
Project Leaders: Chris Kealey, Caltech Y & Craig SanPietro, Caltech BSE ‟68, MSME „69
Caltech Students: Rory Perkins, David Rosen & Kevin Watts
Universidad Landívar Student: Saúl (Duque) Arriaza