Reimagining Infrastructure: Converting Defunct Rainwater Tanks into Sanitation Assets
The Problem
An example of a household’s rainwater storage tank, open to the elements and contamination.
In many rural parts of Tanzania, households have long relied on underground rainwater storage tanks for domestic water supply. These tanks, built decades ago using locally available materials, vary widely in size—from as little as 1,000 litres to over 50,000 litres. Their construction was often a community-led response to the lack of reliable piped supply. They allowed families to store rainwater during the wet season and use it for drinking, cooking, and washing through the dry months.
Today, however, these tanks pose a new set of challenges. Most are unlined, uncovered, and vulnerable to contamination. As a result, they have contributed to high rates of waterborne disease, including diarrhoea and cholera. In areas where DMDO has now introduced piped, metered water, these tanks continue to be used during the rainy season—both out of habit and to avoid paying for water. This continued use reduces consumption from the safe water system and undermines cost recovery.
An example of an unimproved pit latrine.
At the same time, household sanitation remains limited. Many families rely on unimproved pit latrines, often located close to living areas or shallow wells. Upgrading sanitation is a national priority, but progress is slow, particularly where new latrine construction is costly or land availability is limited.
DMDO is now exploring a potential solution that links these two issues: converting old rainwater tanks into improved toilets. The idea is to repurpose existing underground infrastructure that is no longer safe for water storage, and instead use it as a sealed containment structure for household sanitation.
Understanding the Fit: Why Water Tanks May Serve as Sanitation Infrastructure
In Nambahu village, Athumani Mega Kupewa, 64, and his wife, Somoe Chande, 61, built an improved latrine that meets basic hygiene standards at a cost of $300. Their new facility is safe, private and easy to clean. More importantly, their health has significantly improved, with far fewer cases of stomach infections. The money once spent on medical treatments is now used for other essential family needs.
An improved toilet in this context typically includes:
A washable, non-permeable slab
A water-sealed pan, such as a SATO, to reduce smell and prevent fly access
A sealed underground pit or chamber for waste containment
A durable and private superstructure
Safe distance from water sources and living areas
Underground rainwater tanks already offer many of the characteristics needed:
They are watertight and structurally contained
They have significant storage capacity
They are already located within household plots, often close to the home
They are underused or no longer safe for their original purpose
By adapting these tanks to serve as waste containment chambers—similar to a septic tank or improved pit—the infrastructure can be reused rather than abandoned. This reduces the need for new excavation or construction, and provides a way for households to incrementally improve their sanitation status using existing materials.
Technical Requirements and Conversion Process
A watertight and structurally contained rainwater storage tank with clearly contaminated water.
A rainwater storage tank that could be repurposed to improve a household’s sanitation.
The conversion of a rainwater tank into a sanitation system involves several technical steps:
Assessment of the tank
The tank must be structurally sound and watertight. Tanks with major cracks or leakage cannot be used without significant repair.
Location must be assessed to ensure safe distance from shallow wells or surface water.
Access modification
Most tanks have narrow hatches. These must be widened and reinforced to allow installation of a concrete slab and toilet pan.
Slab and pan installation
A standard latrine slab, often made of concrete, is placed above the tank opening. A SATO pan is fitted to create a water seal and improve hygiene.
Ventilation and superstructure
Proper ventilation is required to allow gas release. A vent pipe with fly screen may be added.
A shelter is constructed above the slab to ensure privacy and weather protection.
Sludge management planning
Larger tanks (typically >5,000L) may be emptied periodically using vacuum tankers.
In areas without emptying services, twin-pit conversion or composting solutions may be considered instead.
This process is not appropriate for every tank. Some may be too small, too shallow, or too degraded. Others may be too close to a water source or located in an area where regular emptying is not viable. Each conversion must be considered on a case-by-case basis.
Implementation Approach
DMDO is beginning this work by identifying suitable pilot areas where:
Households continue to use old tanks for rainwater despite access to safe water
Household sanitation remains poor
Structural assessments show a high number of tanks in serviceable condition
These areas will form the basis for pilot projects to test the technical feasibility and community uptake of the approach. The work is being carried out alongside DMDO’s savings group programme, which can offer households a way to finance improvements over time.
Community engagement is critical. While the idea is practical, some households may need reassurance about converting former water infrastructure into sanitation facilities. DMDO is developing sensitisation and training materials as part of its sanitation marketing programme.
Why This Matters
This is not a solution for every context. But where conditions are right, it offers a way to make use of legacy infrastructure that would otherwise sit unused or pose a health risk. It also reduces the cost and complexity of constructing new latrines from scratch.
If successful, the model could be replicated in other areas where rainwater tanks are common, and where piped water has rendered them redundant. It represents a practical, incremental step toward improving sanitation coverage—and reducing reliance on unsafe water—without major capital works.
DMDO is continuing to develop technical guidelines and assess pilot sites. Updates will be shared as the work progresses..
