Volunteers from Engineers Without Borders construct a rainwater harvesting system for a remote village in the Peruvian Amazon

By Jennifer Roath, P.E.

The Amazon River basin is the largest in the world, spanning 40 percent of South America and discharging an average 55 million gallons of water per second into the Atlantic Ocean. When the Amazon River flows out of Peru, it only has one-fifth of the final discharge, yet it is still greater than any other river in the world. Despite this massive water resource, industrial and agricultural runoff, combined with insufficient sanitation practices, have unfortunately contaminated the region’s water supply.

Without access to water treatment systems, the 105 inhabitants of Mariscal Castilla, a small Peruvian village located at the headwaters of the Amazon, send family members to the river each day to fetch buckets of water. After drinking this water, they often suffer from debilitating water-born illnesses, leading to missed work or school. Starting in 2017, a team from Engineers Without Borders Central Houston Professional Chapter worked with this village to address its needs and provide a sustainable alternative to drinking untreated stream water.

Designing a Solution

In September 2017, a small group of engineers from our chapter traveled to Mariscal Castilla. There they discussed challenges with village leadership, collected data and surveyed the landscape. After gathering as much information as possible, the team regrouped in Houston and spent the next year assessing options and generating design plans.

Bacteria and E. Coli testing confirmed the streams around the village were contaminated and would need treatment if selected as the project’s water source. And, despite the region’s available ground water, many nearby villages have abandoned their wells due to the undesirable taste. In order to pump and treat either water source, a reliable energy supply was critical. Confined by dense jungle, Mariscal Castilla is only accessible via the Amazon River, limiting resource options for the design.

Furthermore, the villagers would need to independently operate the system. Past projects have shown that complicated technology that requires expensive repairs is eventually abandoned; therefore, we decided against a small water treatment plant and groundwater wells as alternatives. Fortunately, the village receives more than 200 inches of rain annually, providing an abundant source of clean water. We determined that installing a rainwater harvesting system and a gravity fed distribution line was the most sustainable solution for this village.

Volunteers lifting the first of three storage tanks onto the tank platform in Mariscal Castilla. Photo: Jennifer Roath

The next step was to calculate tank sizes and identify potential sites. To ensure the entire village has ownership of the rainwater harvesting system, only common buildings were considered as potential locations. At the front of the village, closest to the Amazon River, sat a schoolhouse and meeting space with metal roofs instead of thatching, a prerequisite for rain collection. Taking the combined roof areas and the estimated per capita water consumption, the inputs were compared to local monthly rainfall data to size the storage tanks. To supply the village with 15 liters of drinking water per person per day, three 7,500-liter tanks would be needed. It was assumed that non-drinking water for activities such as washing clothes would still be sourced from the river; therefore, only drinking, cooking, and bathing was used to estimate water usage.

Tank elevation was also a critical design component since the system will be entirely gravity fed. In addition, the heavy seasonal rains inundate most of the village with three to five feet of flood water for months at a time each fall. Homes are built on posts to protect families during these events. This meant our tank platform and filling stations needed to be above the highwater levels too.

The last design consideration was the distance from the homes. The World Health Organization considers “basic access to water” when the taps are between 300 and 3,000 feet from a residence. Since children were often the ones retrieving the water, our team targeted a maximum distance of 500 feet for any family in the village. Given the minimum filling station height set by the flood level, the required tank elevation was calculated to provide sufficient pressure to fill a bucket in less than a minute at a filling station over 1,000 feet away.

After finishing the design and receiving travel approval from Engineers Without Borders USA, we began planning transportation and construction logistics. Constructing the entire system, even with considerable help from the villagers, would take five weeks to complete. Ten of our engineers volunteered to rotate into the village in two week increments to supervise construction, and the first flights were set to take off in October 2018.

Complications Strike

After spending nearly a year drawing detailed plans for the collection, storage, and distribution systems, in July 2018, we received word that a major flooding event had washed away 100 feet of the village shoreline, including our proposed site. The villagers had already started relocating the school and community building, so our best option was to relocate the tanks to this new site. Since a roof is the requisite component on the building, the villagers rushed to construct the frame and install the metal sheeting before our arrival in October.

The rainwater harvesting system in Mariscal Castilla. Gutters along the community building fed the three storage tanks. Underground pipes run towards the schoolhouse to the primary filling station where villagers can fill their buckets and water bottles. Photo: Jennifer Roath

The new tank site was 1,500 feet from the river, and initial reports indicated flooding was only one foot high. However, when our engineers arrived in October, they discovered that the highwater mark was over three feet, meaning the entire system would need to be two feet higher than planned.

The original tank platform design was a manually compacted dirt mound, three feet high with a 1:2 slope. With the help of the villagers, we anticipated mound construction would take three to five days. However, raising the mound to five feet would mean doubling the volume and potentially overrunning the schedule. An alternative wooden platform design was not feasible to construct within the time constraint because harvesting wood is extremely time consuming. This meant we had to stick with the original dirt mound design, despite the additional labor demands and stress on schedule.

Another major complication was the new community building was too short for the tanks. If the roof was left as is, the collection piping would enter the tank at a lower level, reducing storage capacity. After discussions with the community leaders, a skilled group of villagers set out to raise the building’s roof while the rest of the team continued to work on the tank foundation. Using their own technique, the villagers adjusted the roof’s pitch one panel at a time.

To complicate matters further, the seasonal flooding started early in 2018. Our project was a collaborative effort with the village, and we were relying on volunteers to provide a considerable portion of the labor. Each fall, the villagers harvest their rice crops before the rainy season starts. With the harvest schedule in mind, the project was timed for when villagers could help. This year, most villagers were unavailable to help with construction because they were harvesting their rice crops.

We knew the trip would be over in November and our team would not be returning for at least a year. Consequently, during that final week, we made the decision to prioritize the critical components: hang the gutters, connect collection piping, and finish the primary filling station. This would allow the village to start collecting rainwater, even if they had to walk up to 1,500 feet to the site. The distribution portion of the project was postponed until we could make a return trip.


On the penultimate day of our trip, we rushed to get the system operational. We attached the filters at the filling station, covered the overflow discharge pipe with mosquito netting, and placed chlorine tablets in the intake line. Overwhelmed by what seemed like a never ending “punch-list,” we barely noticed the sky darkening overhead. Just as the men attached the final gutter, rain started to pour over the site. We huddled together under the roof, watching as water flowed from the gutters. We could hear the rush of the water reverberating inside the tank as it started to fill.

Thirty minutes later, the clouds cleared, and we gathered eagerly at the filling station with empty bottles in hand ready to test the system. Taking turns opening the valves, the clear water flowed into our water bottles. As the villagers had their first sip of freshly harvested rainwater, we were all beaming with joy. The next day, our team packed up and departed Mariscal Castilla.

Over the last eight months, the villagers have sent word that the system is collecting rainwater. They are already seeing the health benefits of the cleaner water and reporting fewer illnesses. This fall, our team will be returning to Mariscal Castilla to help install the distribution piping and complete this meaningful and impactful project.

Jennifer Roath, P.E., is a water conveyance engineer at Lockwood, Andrews & Newnam, Inc. (LAN), a national planning, engineering and program management firm. She can be reached at JARoath@lan-inc.com.