Investigation of the sources of pollution of harvested rainwater at household level: A case of Makoka sub ward, Makuburi Ward, Dar es Salaam

In many parts of the world, when the sky opens up, people do not let the water run off into the streets. Instead, they catch it on their roofs, guide it through pipes, and store it in large tanks for later use. This practice, known as rainwater harvesting, offers a lifeline in areas where tap water is scarce or expensive. The water falling from the clouds is naturally clean, but once it touches a roof, travels through a gutter, and sits in a container, its quality can change. The concern for scientists and public health officials is not the rain itself, but what happens to it after it lands. If the collection system is not maintained, the water can pick up dirt, animal droppings, and harmful bacteria, turning a vital resource into a health risk. Understanding exactly where this contamination comes from is the first step toward keeping the water safe for drinking and cooking.

A recent investigation in the Makoka sub-ward of Dar es Salaam, Tanzania, set out to find the specific sources of pollution in household rainwater systems. The researchers focused on a community where residents rely on harvested rainwater to supplement the municipal supply, often due to long periods of water rationing. By visiting twelve households and observing their setups, the team discovered that the water was rarely dirty because of the rain, but rather because of how the systems were built and maintained. The most common culprit was the roof itself. When rain first hits a roof, it washes away accumulated dust, bird droppings, and leaves. In the homes studied, 83 percent of the residents identified this initial wash-off, or roof deposition, as a major source of contamination.

The problem often continued as the water moved from the roof into the storage tank. The study found that gutters and the pipes connecting them to the tanks were frequently in poor condition. About 42 percent of the roofs were in bad shape, and 33 percent of the gutters and pipes were deteriorated. These cracks and leaks allowed outside dirt to mix with the clean water. Furthermore, the storage tanks themselves were often compromised. Physical inspections revealed that many tanks had cracks or leaks, which could let in groundwater or surface runoff. Despite these visible risks, maintenance was lacking. Only 17 percent of the households cleaned their storage tanks regularly. In fact, one-third of the residents admitted they had never cleaned their tanks at all, while half said they did so only rarely.

Another significant issue was how people accessed the water once it was stored. In 42 percent of the homes, residents used unsafe methods to draw water, such as dipping buckets directly into the tank. This practice introduces germs from hands and containers into the supply. In contrast, the other 58 percent used taps or pumps, which kept the water sealed and protected. The study also looked at the environment around the houses. A striking 75 percent of the homes had trees overhanging their catchment areas, dropping leaves and debris into the system. Yet, only 33 percent of these households had any device to screen out the leaves.

The residents were aware of the need to filter out the first, dirtiest batch of rain, known as the first flush, but they struggled to do it consistently. While 75 percent considered this practice important, only 17 percent actually performed it every time it rained. Most who tried to do it had to manually disconnect the pipes to divert the water, a method that is easily forgotten or skipped. The researchers concluded that the pollution was not an inevitable result of harvesting rain, but a consequence of inadequate maintenance and simple design flaws.

To address these issues, the study proposed practical engineering solutions that do not require complex technology. The author suggested installing an automatic first-flush interceptor, a simple device that captures the initial dirty water and lets it drain away before the clean water enters the tank. They also recommended using screens to block leaves and providing ladders to make it easier for people to climb down and clean their tanks. For the water that is already stored, the researchers noted that boiling it for at least twenty minutes is a reliable way to kill harmful bacteria, though this requires fuel and time. The path forward, they argued, lies not in finding new water sources, but in fixing the old ones: repairing roofs, sealing tanks, and establishing a routine of cleaning to ensure that the rainwater remains a safe and dependable resource for the community.