Kilimoerevu by team GreenForce

Unlocking the Potential of Rainwater harvesting and Wastewater re-use

Welcome to GreenForce, a startup team of both master’s and undergraduate students from Jomo Kenyatta University of Agriculture and Technology in Kenya with the goal of optimizing the process of rainwater harvesting and wastewater reuse targeting households in Kenya and globally.

Rainwater Harvesting

Rainwater is arguably the most accessible and sustainable source of water in the world. Rainwater falls on the roof of the building where it is used, so everyone has access to rainwater without expensive costs. A roof is a non-trafficable surface so there are few opportunities for contamination. Rainwater is simple to manage and treat at a low cost. Rainwater harvesting is most efficient as part of an integrated water management approach with multiple water sources for seasonal water security. The rainwater harvesting at a local scale has a profound impact on stormwater management at the metropolitan level, reducing the volume, peak flow and contaminant levels in stormwater.

According to UN reports rainwater harvesting could end much of Africa’s water shortage. The reports considered Africa as not water scarce. The rainfall contribution is more than adequate to meet the needs of the current population several times over. The report stated that Kenya would not be categorized as a ‘water-stressed country’ if rainwater harvesting is considered. The water crisis in Africa was found to be more of an economic problem from a lack of investment and not a matter of physical scarcity.

What Kenya needs to do to save its population from hunger and water-related problems using its gold in the form of rainfall

According to the 2019 household and population census, there is a total of 12 million conventional households in Kenya. Of these households, 3.9% translates to 469,678 households engaging in rainwater harvesting. To layout the rural-urban status, 79%(368,964) of these households are rural-based and 21%(100714) are urban-based.

In Kenya, largely due to recurrent droughts, over 3 million families that rely on crops and livestock are threatened and thousands of people die each year as a result of thirst and hunger. With the Kenyan population being projected to grow drastically in the next few decades and climate change being a global issue, clean water provision will be an even greater task.

It is good to note that Kenya receives heavy rainfall annually which is characterised by heavy flooding and landslides. This further leads to the loss of lives and livelihoods.

How do we then mitigate this challenge?

We can only avoid these water challenges by adopting smart ways to manage the rainwater that the country receives so as to ensure that the existing households benefit from it rather than die from it. This team, therefore, proposes a smart approach to rainwater harvesting and wastewater re-use which will have less financial implications for the end-user.

To achieve this, we have developed a platform that provides information and the technical know-how on how to implement rainwater harvesting and re-use at the household level. This platform by the name KILIMOEREVU has the following functionalities:

  • Provides an overview of the current situation in Kenya in terms of drinking water sources and basic sanitation
  • A data entry point which is comprised of the selection of the residential area, entry of the roof area, entry of the size of the water tank, entry of the domestic water use per day in litres and entry of the proposed irrigation area size. There are two ways of selecting the roof area which are either by measuring it manually or using google maps to estimate the roof area and perimeter which are provided in the application.
  • A calculator which gives the analysis and results to the user based on the entered data.
  • Costing which estimates the tank prices based on the entered volume.
  • Contact details where one can reach us at their convenience.
  • The platform also has the virmifiltration section which is the proposed method of wastewater filtration and re-use.

The application is as outlined in the following screenshots


Wastewater treatment and reuse is one of the most promising efforts to stem the global water crisis. The main motive of green technology is to provide high-end results without compromising on environmental sustainability. Vermifiltration is an extension of the vermicomposting process. It is a biofilter with earthworms digest the suspended particles screened on a filter bed degrade organic matter through enzymatic activity and in the process of ingestion they passively aerate the system by burrowing action and remove pathogens. It results in useful products, treated clear water for reuse purposes and vermicompost which can be used in agricultural fields as organic manure. It is an extension of soil filtration with earthworms to speed up the decomposition process to utilize organics to produce fresh manure. Wastewater passes through the active layer where organic matter is converted into humus enriched vermicompost by earthworms. Filter media supports the growth of micro-organisms and subsequently, secondary treatment occurs. The grinding activity of earthworms helps in increasing the total surface area present in the filter media, enabling higher absorption of organic and inorganic contaminants from the wastewater. Dissolved and suspended particles are trapped in the filter media as they percolate and are stabilized through complex bioprocesses that take place in the active layer. Dissolved components of wastewater move further down in the profiles absorbed into the surface matrix media and are degraded by the symbiotic action of earthworms released enzymes and microbes. Vermifilter does not clog because earthworms improve aeration by burrowing action and accelerate microbial activity increasing the population of soil micro-organisms thus increasing utilization of organisms.

Design parameters

Hydraulic loading rate – it is the application of wastewater to the unit area of the vermibed for unit time.

Hydraulic retention time – it is the time of interaction of wastewater with the filter media in which earthworms reside.

Stocking density – refers to the population of earthworms applied to the bed. Earthworms bigger in size can treat more efficiently compared to smaller ones due to their voracious eating habits. Optimum stocking density lies between 15,000 and 20,000 worms/m3.

Earthworms survive best at the PH range of 6.2 to 9. A temperature of 25-27 degrees Celsius is the optimum range for the activity, growth and reproduction of epigenic earthworm species. Earthworms need a suitable dwelling habitat to thrive upon and perform their activity.

To design the ideal filter media different materials will be utilized such as river bed gravel, stone chips and sand. This filter media also influence the establishment of microbial biofilms and microbial community structure within the complex vermi-ecosystem and treatment performance. The operational and environmental conditions play an important role in vermifiltration process.

The process of rainwater harvesting and wastewater re-use overview

This video shows the detailed process of rainwater harvesting and its storage and details the process of using the water in the household for activities such as kitchen washing and bathing. It also outlines how the intended wastewater is filtered through virmifiltration, stored and used. It also shows a small smart garden where the purified wastewater is used for irrigation of crops such as vegetables.

For the water and wastewater, plumbing inside an existing house will need retrofitting but for new houses, the plumbing should consider harvesting and recycling.

Impact and the way forward into the future

This solution has the potential to not only make households’ water sufficient but also ensure that the households are food secure by eating fresh produce from their gardens as the platform provides information on how irrigation can be done using filtered wastewater. It will also ensure that floods are on a minimal scale and drought and hunger are a thing of the past. Since the virmifiltration process uses compost to produce worms used in the process, households will benefit better as they will use the compost waste they produce in the process hence leading to a positive reduction of environmental pollution. The value of sustainability has increased drastically in the last decades and our solution can provide a direct contribution to 3 out of the 17 UN sustainable development goals namely:

  • Clean water and Sanitation
  • Climate Action and
  • Zero hunger

Going into the future, we would also like to market our kilimoerevu application to businesses dealing with rainwater tanks and irrigation. We are also open to advertising different businesses that deal with rainwater harvesting, wastewater re-use and irrigation.

Our team

GreenForce. We are a multidisciplinary team of 5 students studying in Kenya at the Jomo Kenyatta University of Agriculture and Technology and our different course backgrounds were a real asset in helping tackle this problem and coming up with viable solutions to the problems facing humanity.

Contact Us

This can only be the begging for us and our future is surely a shining star. If you would like to know more about us, feel free to reach out to us at these addresses:

Samuel Wanjiru:

Mercy Chepkorir:

Festus Malombe:

Lorrain Eyinda:

Lena Anyango: anyangoonyangolena@b-ke

We are especially looking for assistance in finances as well as guidance from those knowledgeable in rainwater harvesting, irrigation and wastewater re-use to help us disseminate this information in Kenyan homes to enable them get access to clean, safe and sustainable water supply.