Catching Rainwater And Opportunity In Kabwe, Zambia

By Will Forester. 01/10/2021

Kabwe may be the most toxic town in the world. It was founded in 1902 when lead and zinc deposits were discovered. These deposits have now been mined and smelted for over 100 years with almost no safeguards or restrictions on use of waterways that carry waste. And the effect on thousands of people in the surrounding communities is devastating. In the most affected townships, lead in soils measures 10 times the United States safety limit. There is a desire to clean-up the area, but the effort will be massive and take years. In the meantime, one way to avoid the lead found in the water there is to avoid ground sources and instead catch rainwater.

Mr and Mrs Moono own Farm Number 37B in Mpima Dairy Scheme, Kabwe, about 450 kilometers from Monze. Monze is where we trained local communities members in February to build rainwater catchments, BioSand Water Filters, and Interlocking Stabilized Soil Bricks. The Moonos heard about the training and inquired with our Monze Coach, Warren Mwenda about an opportunity to contract with him and a team to construct two tanks on the Moono’s farm.¬†Arrangements were made and soon our Coach and masons Saiti Chiboola, Friday Ng’andu, and Richard Mwiinga were heading north to build two tanks on Farm 37B (all the masons participated in our original training).

Fortunately, the Moono’s farm land does not appear to contain harmful levels of lead. But any water that enters his land runs the risk of bringing lead with it. He uses a borehole and a diesel-generated pump. Not only is the diesel expensive, but boreholes have a habit of running dry or becoming contaminated, as we were shown in Monze. This seemed like a great opportunity to expand the use of Rainwater Catchments in the area (who knows how many others will see the tanks and inquire about them), create more safe water and water security, and acquire additional Rainwater Catchment Tank construction experience for our Coach and the masons.

Over the course of many days, two 20,000 liter tanks were built. Warren did an outstanding job of documenting the construction process in both pictures and video. And this is how it all unfolded.

Building The Foundation

After arriving the first thing the team did was site the exact location for the tanks next to the building roof (gutters for the roof are still waiting to be installed). They then excavated the top soil to create a leveled base upon which to build the foundation.

Kabwe rainwater catchment foundation

With the external foundation of bricks and mortar laid, the team dug out and laid a cross-pattern of bricks to finish the foundation. Although, Interlocking Stabilized Soil Bricks were not used in either the foundation or walls of these tanks, they can be. In fact, our Programs Manager, Eric Lijodi is testing curved bricks to be used as Rainwater Catchment Tank walls right now. 

Kabwe rainwater catchment tank foundations
Kabwe rainwater catchment foundation cross 2

Pouring The Slab

After constructing the foundation with bricks and mortar, the inside gaps were filled with compacted hardcore and mortared to create a level base. They cut and laid a mesh wire base for added support, aligned the delivery pipe, and then poured a floor slab.

Once the floor slab was poured and smoothed it was left to set for at least 12 hours. At this stage it’s satisfying to see the Rainwater Catchment Tanks start to rise out of the ground. It’s important to get the cement mortar mix right and to ensure the mortar remains damp for at least two weeks to prevent cracking.

Kabwe rainwater catchment foundation complete 2
Kabwe rainwater catchment tank foundation complete

Building The Walls

With the slab finished, they set about creating the wire mesh mold that would form the walls. The wall mesh was attached to the mesh laid under the slab and then wrapped with reed mats to form a strong cylindrical shape upon which the mortar will be pressed. As you can see from the ladders, first mortar was hauled into the tank, with one or two coats being pressed to the inside wall. Once they finished establishing a firm structure with those layers, they removed the mats from the outside of the tank and started to mortar there. The height of these Rainwater Catchment Tanks is usually anywhere from 1.5 to 2.5 meters. Anything taller places more stress on the walls than they may be able to resist.

Kabwe rainwater catchment tank chicken wire walls
Kabwe rainwater catchment tank prepped walls
Kabwe rainwater catchment tank inside wall mortar 2
Kabwe rainwater catchment tank chicken wire walls
Kabwe rainwater catchment tanks mortared walls
Kabwe rainwater catchment tank wall finishing touches

These videos show the tank walls taking shape.

The previous night it rained – before the Rainwater Catchment Tank roof was installed and before the walls were mortared. As you can see, they did a great job with the slab and fittings. It works!

And Finally, The Roof

The next step was one up. Onto the roof! First, they measured, cut, and formed a wire mesh. Then they built a structure inside of the tank made of wood branches and covered it with support and the wire mesh. Mortar was then pressed to create a cover or top. After the mortar cured for a while, it was trimmed to create a neat top. And that’s it. Coach Warren, Saiti, Friday, and Richard said a fond farewell and headed back to Monze. But not before Mr Moono shared his thoughts on Rainwater Catchment Tanks. We look forward to hearing about more opportunities to deploy this technology in all areas were water security is or could be compromised.

Kabwe rainwater catchment tank roof mortar
Kabwe rainwater catchment tank drainage pipe hole
Kabwe rainwater catchment tank field
Kabwe rainwater catchment tank finished interior
Kabwe rainwater catchment tank finished
Kabwe rainwater catchment tank masons goodbye 3

I am, in the first place, very happy.

-Mr Moono

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