Water and construction in Rwanda

(Guest post)

Access to water is typically considered in the context of domestic use, i.e. the access of individual households to meet their daily water needs, but water can also have a significant impact on the construction of buildings and infrastructure. A lack of access to water can raise construction costs, influence the choice of materials or the time when one can build, and necessitate increased manual labor. In other words, it can fundamentally affect people’s ability to build (both for shelter and for development), which, in addition to having clean water for household use, is a basic human need.

In 2011-2012, I spent a year practicing architecture in Rwanda, the majority of which was spent in a small village in the northwest part of the country. My firm had recently constructed a hospital there, but the client also needed us to build new houses in order to attract and retain skilled medical practitioners. Our task was to build houses that would be attractive and comfortable for living, but also durable, seismically stable, related to the local environment, and within certain budget constraints. For these reasons, we chose to build the houses with compressed stabilized earth blocks (CSEBs) as our main building unit.

IMG_9075

House under construction

Due to the particularity of local soil conditions, there is no singular formula one can follow in order to form CSEBs. We had to come up with the correct ratio of materials, using a process of educated guesses combined with trial and error, in order to form strong blocks. According to the results obtained with a handheld pressure-measuring instrument, we selected our best mixes of soil, cement, sand, aggregate, and water and sent them out for more thorough compression testing.

DSCN3555

Getting a hands-on feel for soil and water mixtures

We also calculated our cost per block, and the portion of that cost attributed to each material. We assumed that soil and water would be the least expensive materials because they were freely available natural materials that were coming directly from our site or the adjacent creek, while cement, sand, and aggregate were trucked in, and thus should be more expensive because we had to pay for purchasing the material and for transportation costs (which are high for a remote site in a region with poor dirt roads). However, when we calculated the cost per material, we were surprised to see that the cost of water varied from about 75% to 280% of the cost of the cement across the range of our tested blocks. How could water be such a high percentage?? Surely it should be a small fraction of the cost of the purchased and delivered materials!

img_6492_sm

Women were employed to carry gravel on site, as pictured here, but also would obtain water by walking down to a site in the valley and back

However, we had to take into consideration that virtually all the water we used for CSEB production was collected by women who had to trek down the hill to the creek, fill a container, and carry the water back up the hill to our site. We had two cisterns on site, and it would take eight women all day to trek enough water to the site to fill them. This would happen day after day. So the cost of the labor for retrieving the water, one container at a time, was driving up the cost of the CSEBs, and thus the entire project.

Unfortunately, we had no choice, as we were in the process of building a system to bring piped water to the site, but the system was not yet in place. The cost of water for our construction was something we had to absorb, but for many people living in that region, it could be a significant obstacle. The CSEBs that we were using were a more durable, more seismically stable version of the most common local construction method: hand-made mud blocks, which are a mixture of soil, straw, and water. Water is also needed to make concrete, which is becoming a more common construction material in some areas. Of course, during the rainy season, it is possible to collect all the water needed from the rain, but in the dry season, obtaining water to rebuild a collapsed retaining wall or make necessary repairs to a home becomes significantly more difficult.

0context_IMG_0752

Local construction with mud blocks, typical in this region

0context_IMG_6497

Vernacular preparation of mud blocks

The irony of the situation is that we were working in a place that has two rainy seasons a year, and when it rains, it rains heavily. So at the same time that we were dealing with the high costs of getting water to the site, we were also working collaboratively with our local engineers to come up with the design for a large retention bioswale that would collect stormwater runoff coming from the ridge of the hill down toward our site. The new road that we had built for vehicular access to the housing site necessitated the construction of this bioswale in order to prevent flooding and washing out the neighbors’ homes and lots. We also had to build drainage gutters and culverts along the side of the road to collect the water.

This is the flipside of water issues when designing buildings and landscape, which is that in addition to providing water, it is critically ethical to ensure that you deal with any excess water. Erosion is a major concern in Rwanda due to deforestation and a primarily hill topography. Water runoff depletes the topsoil in a country that is already stretched thin in the proportion of arable land to population density, and runoff can also pollute drinking water sources (which are often the streams in the valleys below people’s homes). Thus, we had to make sure to carefully consider the larger impacts of our construction on stormwater drainage in the area surrounding our site.

BDH_soakaway_garden_area

New road gutters leading to the bioswale site (to be excavated on the right, in front of the tree with red flowers)

When working in any context, but particularly in those where resources may be limited and new construction methods are being tested, it is critical to consider access to water as a factor in building construction. Strategies for dealing with excess water runoff must also be developed. In sum, anyone seeking to build must consider water.