A sewage system is the network of drains, pipes, pump stations, and treatment works that carries wastewater away from a property and makes it safe to return to the environment. It is infrastructure most people never think about until something goes wrong, but the design of the system determines what happens when it does, who is responsible for fixing it, and what you can and cannot put down a drain. This guide explains how a sewage system works, what its components do, and how the picture differs between a serviced suburb and a property on its own septic system.
Why Sewage Systems Matter for Public Health
Separating people from their own wastewater is one of the most effective public health measures ever implemented. Untreated sewage carries bacteria, viruses, and parasites responsible for cholera, typhoid, hepatitis A, and a wide range of diarrhoeal illnesses. The World Health Organization continues to identify inadequate sanitation as a major contributor to preventable disease worldwide.
The same applies at the level of a single property. A leaking sewer line, an overflowing gully, or a failing septic tank puts effluent into soil and groundwater where people and animals come into contact with it. That is why a persistent sewage smell or a recurring backup is treated as urgent rather than cosmetic, and why the environmental consequences of neglect are covered in our article on the environmental impact of poorly maintained drains.
The Components of a Sewage System
The Collection System
Wastewater leaves a property through the internal plumbing and enters the buried drainage that runs to the municipal connection. These lines rely on gravity, so correct fall matters more than pipe diameter. Older properties may still have salt-glazed clay or fibre-cement pipework; newer work is generally uPVC. Where gravity alone cannot do the job, a pump station lifts the flow to a higher point so it can continue to run downhill. Our guide to sewerage lines for homeowners covers where responsibility for these lines begins and ends.
Sewers Versus Stormwater Drains
This distinction matters and is widely misunderstood. Foul sewers carry wastewater to treatment. Stormwater drains carry rainwater and discharge, usually untreated, into the nearest watercourse or the sea. Anything tipped into a stormwater drain, from paint to cooking oil, effectively goes straight into the environment. Illegally connecting a gully or downpipe across the two systems overloads treatment works in wet weather and causes overflows. We cover the difference in detail in sewer drains versus storm drains.
The Treatment Works
This is where wastewater is processed before it is released. Treatment works are operated by the municipality, and their capacity and condition determine how much of the incoming load can actually be treated to standard.
How Does a Sewage System Work, Stage by Stage?
Sewage treatment is conventionally described in three stages, each removing something the previous stage could not.
- Preliminary and primary treatment. Screens remove rags, wipes, and debris, and grit chambers drop out sand and stones. The flow then passes into settling tanks where heavier solids sink as sludge and fats and oils are skimmed off the surface. This stage is purely physical, and it removes a substantial share of the suspended solids.
- Secondary treatment. This is the biological stage. Bacteria and other microorganisms are given oxygen and time to consume the dissolved organic matter that settling cannot remove, typically in aeration basins or trickling filters. The biomass is then settled out. Secondary treatment does the bulk of the work of making the effluent safe.
- Tertiary treatment and disinfection. Where a higher standard is required, filtration and nutrient removal strip out remaining solids, nitrogen, and phosphorus. Final disinfection using chlorine or ultraviolet light deals with residual pathogens before discharge.
Treated effluent is then released to a river, wetland, or marine outfall. Some works recover the sludge for use as fertiliser or capture the biogas it produces to generate electricity, and some treated water is reused for irrigation and industrial purposes rather than discharged.
Centralised and Decentralised Systems
A centralised system is what most urban South African properties are connected to: municipal sewers running to a municipal treatment works, funded through rates and service charges. The property owner is responsible for the drainage on their side of the connection point, and the municipality for everything beyond it.
A decentralised system treats wastewater on the property itself, which is standard on smallholdings, farms, and estates outside the reticulated network. Here the owner carries the full responsibility, including desludging on a sensible schedule. If your property runs on one, our guides to how septic tanks work and septic tank regulations in South Africa set out both the mechanics and the legal obligations.
Common Problems and Maintenance
Most faults on a sewage system originate on the property, not at the treatment works. The recurring causes are:
- Fats, oils, and grease poured down kitchen drains, which congeal and narrow the bore. Commercial kitchens are legally required to intercept these before they reach the sewer.
- Wet wipes and sanitary products, which do not break down in the way toilet paper does and are a leading cause of blockages and pump station failures.
- Tree root ingress through joints and hairline cracks, which is the most common structural cause of failure on established properties.
- Ageing pipework that has become brittle, lost its fall through ground movement, or partially collapsed.
Slow drainage across several fittings at once, gurgling, or a smell that keeps returning after cleaning generally means the fault is in the buried line rather than the fitting. Our guide to unblocking a sewage drain covers what is reasonable to attempt yourself and where a camera survey is the sensible next step.
Pressure on South African Sewage Infrastructure
Much of the country’s sewer network and treatment capacity was laid down decades ago and is now carrying loads it was never sized for, in areas that have grown considerably since. Ageing infrastructure, power interruptions affecting pump stations, and maintenance backlogs all contribute to overflows and to effluent reaching watercourses before it has been fully treated. Cape Town’s stormwater and sewer networks are separate systems for exactly this reason, and keeping them separate is part of how the load is managed. The broader picture is covered in our article on drainage systems in urban areas.
At property level the practical response is straightforward: keep fats and non-flushables out of the system, deal with root ingress before it fractures a pipe, and treat recurring blockages as a symptom rather than an inconvenience.
Getting Help With a Sewage Problem
Drain Blasters works on the property side of the sewage system across Cape Town: high-pressure jetting, CCTV surveys to locate faults precisely, root extraction, septic tank and conservancy tank emptying, and liquid waste removal under the required disposal documentation. If a line keeps blocking or you have a smell you cannot trace, see our drain clearing services in Cape Town and we will establish what is actually happening underground before anything is dug up.
