Water flows easily from the tap in many homes across Nairobi. A glass is filled, a kettle boils, and the assumption is simple: the water is "fresh."

But few people stop to ask a more complicated question.

Where exactly does the water come from before it reaches the tap? And what happens to the water after it leaves the toilet, the sink, or the drainage channels outside the house?

In cities where sewage systems are strained or poorly planned, the journey between waste water and drinking water can become dangerously close.

During heavy rains, some water pumping stations delay supplying water because runoff and sewage mix in drainage systems. Treatment plants may filter the water before it is redistributed, but the question remains: is treatment alone enough when sewage systems themselves are failing?

Understanding the sewage problem in Kenya requires looking at both sides of the city — from affluent estates to informal settlements — because both experience its effects, though in very different ways.

What sewage actually means and why it matters

Sewage refers to wastewater that carries human waste, household waste, and other contaminants away from homes, industries, and public spaces.

It includes water from:

toilets

bathrooms

kitchens

drainage systems

storm water runoff

In an ideal system, sewage flows through underground pipes to treatment plants where harmful bacteria, chemicals, and solid waste are removed before the water is released back into rivers or reused safely.

When the sewage system fails, however, contaminated water can mix with the environment — and sometimes even with sources of drinking water.

This is where the real danger begins.

Why sewage problems affect the poor and the rich differently

Poor neighbourhoods often experience sewage problems more directly.

In some informal settlements, drainage channels run openly through the streets. Wastewater mixes with garbage and stagnant water, creating an environment where contamination spreads easily.

In contrast, wealthier neighbourhoods may have underground sewer lines and better waste management systems. However, even these areas are not immune. When municipal infrastructure becomes overwhelmed, sewage backups can still occur.

The difference lies in exposure.

Residents in higher-income areas may encounter sewage problems occasionally. Residents in lower-income areas may live with them daily.

This gap highlights how infrastructure inequality shapes health risks across urban communities.

Why flooding sewage is common in some Nairobi neighbourhoods

Certain areas of Nairobi have long struggled with inadequate sewage infrastructure.

In neighbourhoods such as:

Donholm

Umoja Estate

Kayole

Embakasi

residents sometimes report sewage flooding homes during heavy rains.

This happens when drainage systems are blocked, sewer pipes are undersized for growing populations, or informal housing develops faster than infrastructure can support it.

Water flowing through streets during storms can carry sewage into houses, compounds, and public spaces.

When this water lingers, it becomes a breeding ground for bacteria and disease.

Why informal settlements face the highest risk

In densely populated informal settlements like Kibera and Mathare, sanitation infrastructure is often limited.

Drainage trenches sometimes run alongside homes, carrying waste through narrow pathways used by residents daily.

When rainfall increases, these open channels overflow.

Children may play nearby. Residents may walk through the water on their way to work or school.

In such environments, sewage contamination is not an occasional hazard — it becomes part of everyday life.

This proximity to untreated waste increases the risk of disease outbreaks.

How sewage contamination threatens drinking water

Heavy rainfall often increases contamination risks because stormwater mixes with waste from blocked sewer lines.

Some water suppliers temporarily reduce pumping during intense rains because treatment plants must process heavily polluted water before distribution.

Although treatment processes remove many harmful elements, concerns sometimes arise about whether overwhelmed systems can maintain consistent water quality.

When untreated sewage mixes with rivers, groundwater, or reservoirs, bacteria and parasites may spread through water sources.

This contamination can lead to outbreaks of waterborne diseases.

Common diseases linked to contaminated water

Water contaminated with sewage may carry harmful microorganisms responsible for diseases such as:

cholera

typhoid

dysentery

hepatitis A

diarrhoeal infections

These diseases spread easily when people consume untreated water or come into contact with contaminated surfaces.

Children, the elderly, and individuals with weakened immune systems are particularly vulnerable.

Outbreaks are more common during rainy seasons when flooding increases the likelihood of contamination.

Why the rainy season increases health risks

During the long rains, urban drainage systems face extreme pressure.

Blocked drains, overflowing sewers, and floodwater mixing with waste create conditions where bacteria spread quickly.

In neighbourhoods where sewage flows near homes or streets, rainwater can carry contaminants directly into living spaces.

The risk becomes especially high when residents rely on shallow wells, water vendors, or unregulated water sources.

This is why waterborne disease outbreaks often coincide with heavy rainfall periods.

Protecting households from waterborne diseases

While large infrastructure solutions are necessary, households can still take precautions.

Common protective steps include:

boiling drinking water during high-risk seasons

storing water in covered containers

washing hands frequently with clean water and soap

avoiding contact with floodwater where possible

Communities can also help by keeping drainage channels clear and reporting sewage leaks to local authorities.

Preventive habits cannot replace proper infrastructure, but they reduce immediate health risks.

Understanding the root cause and long-term solution

Kenya’s sewage challenges are not caused by a single factor.

Rapid urban population growth, aging sewer networks, blocked drainage systems, and unplanned housing developments all contribute to the problem.

In many cases, sewage infrastructure designed decades ago now serves populations several times larger than originally planned.

The long-term solution requires investment in modern sewage treatment plants, expanded sewer networks, and urban planning that keeps pace with population growth.

Without these upgrades, cities will continue struggling with the same cycle of flooding, contamination, and disease outbreaks.

What Kenya’s sewage problem reveals about urban health

Sewage infrastructure often remains invisible — buried underground and ignored until something goes wrong.

Yet its impact reaches every part of urban life.

When systems fail, poorer neighbourhoods experience immediate exposure to contaminated environments, while wealthier areas face indirect risks through polluted water sources and overwhelmed treatment plants.

This imbalance shows how sanitation is not just an environmental issue but also a public health and urban planning challenge.

If clean water is a shared necessity, then sewage management must become a shared priority.

And perhaps the deeper question becomes unavoidable.

If cities continue expanding without strengthening the systems that manage waste, will treating contaminated water be enough — or will the future demand a complete transformation of how sewage is managed from the moment it leaves the household?

FAQs

What causes sewage flooding in urban areas?

Sewage flooding usually occurs when drainage systems are blocked, sewer pipes are too small for the population they serve, or heavy rainfall overwhelms the infrastructure.

Why are waterborne diseases more common during the rainy season?

Floodwater can mix with sewage and carry harmful bacteria into drinking water sources, increasing the spread of diseases like cholera and typhoid.

How can households reduce the risk of contaminated water?

Boiling drinking water, storing water safely, washing hands regularly, and avoiding floodwater exposure can help reduce the risk of waterborne infections.