Designing for Water: Lessons from Namupa

1       Introduction

This article looks at the Namupa water system as a case study in how design decisions are made in rural water supply. It explores the three essential objectives of technical soundness – quality, quantity, and delivery – and considers how those objectives interact with financial viability. It also examines what happened when circumstances changed, what remedies were put in place, and what reflections DMDO draws for the future.

The themes are not unique to Namupa. They touch on challenges that will recur across many systems: how to judge when protective works are needed, how to manage distribution when demand rises, and how to design for growth without tying up scarce capital. By presenting both the original decisions and the adjustments now required, the article illustrates DMDO’s commitment to transparency, reflection and continual improvement in an imperfect world.

2       The Principle of Good Design

At the heart of every rural water project lies a deceptively simple principle: a system must be both technically sound (a system that can consistently provide safe water, in enough volume, and at sufficient pressure to reach households) and financially viable (the water system can generate enough income for its long-term maintenance and potential expansion).

That means two things. First, the engineering has to work –  the water must be safe to drink (Quality), there must be enough of it (Quantity) and it has to reach people where they live (Delivery). Second, the finances have to add up — the local water committee needs revenue to keep pumps running and pipes repaired and, in our case, DMDO needs secure income to cover its own costs and reinvest in future projects as part of our cost recovery model.

In practice, striking that balance is not straightforward. Donor funds are limited, the landscape and community needs shift quickly and no one has the luxury of perfect foresight. Good decisions are made with incomplete information. Sometimes they hold up well. Sometimes they need revisiting.

Namupa Water System is one such case.

3       Building the First System (2021–2022)

In 2021, DMDO committed $163,000 to bring water to three villages: Namupa, Muungano II and Mahiwa. Together they housed just over 5,200 people who were relying on unsafe, unreliable sources.

The design was straightforward:

• An intake weir drawing water from two spring fed streams – one spring nearly 5km away rising in a small village called Nndawa and another rising just 500m from the intake weir;

• Downhill piping to deliver the water from the source (intake weir) to the customers in the villages;

• A 35 m³ storage tank for Mahiwa, 26km from the intake weir;

• 23 distribution points spread across the villages.

The table below shows how the water system design was guided by applying our three engineering principles:

For the first years, the results were encouraging. Water was available and more than 3 million litres per month were delivered. Waterborne diseases dropped.

By any measure, this was a strong start.

4. When Things Changed

4.1 Quality: Turbidity in the Rains

By 2024, farming in Nndawa had expanded. Trees and bushes were cleared, leaving bare soil. When the rains came, water that once trickled clean through roots and vegetation now rushed off the slopes carrying sediment.

At the intake weir, the water turned cloudy. Families noticed. “When the water looks like tea after the rains, my children refuse to drink it,” said Saradina, a mother of two girls and one boy, from Muungano village.

Some households have also reverted to unsafe streams.  This is understandable but it is undoing the ‘behavioural change’ that we worked hard to entrench.

Pupils at Mahiwa Secondary School’s private connection

4.2 Quantity: Still Enough at Source

Meanwhile, demand rose. Mahiwa Secondary School opened with 1,300 students. More than 200 households took private connections.  These were all funded within the communities.  The DMDO effectively mobilised local, private capital to extend water usage beyond the original target customers.

This growth was not anticipated, but it stands as a testament to the success of the system: once water was available, households and schools were eager to connect.

But here’s the important point: the streams themselves were never the problem. Even today, demand is estimated at only about 40% of available flow. There is still plenty of water at source.

The original judgment here on water quantity was sound.

4.3 Delivery: Gravity Reaches Its Limit

The strain came instead on delivery. Gravity alone could not keep up with the higher draw.

From 2024, rationing began. Villages were supplied at different times. Residents cannot access water at any time. They must reserve their place in a queue by leaving a bucket.

“We have a storage tank of 50m3 capacity.  We use this within half a day and must wait till the next day for it to refill due to water rations. That tells us, we need 100,000 litres of water 24 hrs a day to accommodate our demand (i.e. drinking, cooking, cleanness, and gardens) but unfortunately, we are getting a half of it, that really affects our operations.” explained Mr. Honorathi Tarimo, Headmaster of Mahiwa Secondary School.

5. Reflecting on the Decisions

5.1 The Rule of Thumb

In water design, the choice is never between perfect and imperfect. It is between over-engineering (spending too much on risks that may never materialise) and under-preparing (saving money but creating vulnerabilities). The art is to play the facts in front of you, while leaving a little room to adapt.

5.2 Decision Analysis

This challenge of matching today’s needs with tomorrow’s growth is not unique to Namupa. It is a recurring issue across rural water projects, and worth considering in its own right.

5.3 Designing for Higher Demand

When water becomes reliable, demand always rises. Families want household connections, schools expand their use, and overall consumption grows. This is a positive outcome: higher demand means people are drinking more, washing more, and living healthier lives. But it also places pressure on systems that were designed for a different starting point.

The design challenge is how to respond. Over-engineering ties up scarce capital in infrastructure that is not needed straight away. Under-provision carries another risk: if people cannot get the water they need, they fall back on unsafe sources. Some households in Namupa, frustrated by rationing and cloudy water, have returned to nearby streams. This is understandable, but it undoes the behavioural change that the system was designed to secure.

The aim is to size systems close to current needs, but in a way that allows straightforward expansion when demand increases. Chiuta (4,000 pop.) shows this balance. A 75 m³ storage tank was built to be consumed in a day and recharged overnight. That is exactly how the system now operates: it runs at its limit but not beyond it, and upgrades can be justified as connections grow. “One of my roles is to refill the tank, and I do that every day to ensure that water is available to customers when they need it” said Iddrisa, CBWSO’s secretary.

At Lihimilo (1,400 pop.), by contrast, a 50 m³ tank was installed with the same intention of daily turnover, but in practice the community takes three to five days to consume the stored water. The design went too far ahead of demand, leaving capacity under-used. Namupa adds a third perspective: the source has ample headroom, but distribution by gravity alone has reached its ceiling and now requires pumping support.

What these examples show is that it is not always possible to hit the sweet spot. Demand shifts unpredictably, and systems will sometimes be too large or too small. What matters is a consistent approach: design for the demand in front of us, build in pathways for expansion, and adapt when conditions change. Our Water Reinvestment Programme and the long-term commitment of the DMDO to the region allows for this future adaptation.

6. What we are doing now

We are grateful to the Grille foundation, who originally funded the water system four years ago, for funding this evolution. 

We are addressing the issues in the following ways:

7. Lessons We Carry Forward

These interventions are the immediate fixes for a specific problem. But more broadly, what principles should we carry into future designs?

8. Conclusion: Transparency in an Imperfect World

Namupa is a story of choices made with the best knowledge available at the time, some of which have held up well and others which need correcting.

The larger lesson is clear: a water system must be both technically sound and financially viable. That means safe water, in sufficient quantity, delivered reliably. And a financial model that sustains itself.

In an imperfect world, with limited funds and shifting local realities, there will always be risks. What matters is the willingness to be transparent about those risks, to admit when things turn out differently than hoped and to adapt quickly.

That is how DMDO shows itself to be a trustworthy steward of scarce donor resources: not by pretending to be perfect, but by being clear-eyed, reflective and committed to continual improvement.