A water treatment works upgrade is rarely a clean slate. In most of the contracts we have run, the plant was already supplying a town, the existing structures were decades old, and the works had to be rebuilt in stages around an operating process. That constraint, more than any single structure, is what shapes the programme.
This is a working description of what these projects actually contain — written from the ones we have built for UGU District Municipality, uMzinyathi District Municipality, Umgeni Water and Kokstad Local Municipality.
The Treatment Train
Almost every conventional surface-water plant follows the same sequence. Understanding it matters at tender stage, because each stage carries a different construction risk.
- Abstraction: raw water is drawn from a river or dam. This is civil work in a live watercourse — river-level access, temporary works, and a short weather window. At Makhabeleni we built new abstraction pipework as the first element of the upgrade.
- Pre-settling: a settling tank drops the coarse silt load before dosing. On high-turbidity rivers this stage protects everything downstream.
- Flocculation: coagulant is mixed and the flow is gently agitated so fine particles bind into larger flocs. The floc mix channel is a deceptively demanding structure — the hydraulic profile has to be right or the process underperforms regardless of build quality.
- Clarification: flocs settle out. This is where the clariflocculator sits, combining flocculation and clarification in a single circular structure.
- Filtration: rapid gravity sand filters remove what clarification left behind. We built four at Makhabeleni.
- Clear water storage and high lift: treated water is stored, then pumped into the reticulation. At Makhabeleni this was a 500 kl clear water reservoir and a new high lift pump station.
The Clariflocculator
The clariflocculator is the structure most often underestimated. It is a large circular reinforced concrete tank carrying a rotating mechanism, and it has to satisfy three demands simultaneously: it must be watertight, it must be dimensionally accurate enough for the mechanism to run true, and it must be founded to tolerate the loads of a full tank without differential settlement.
At Bhobhoyi, near Port Shepstone, we constructed a clariflocculator along with a pump station, chambers and ancillary structures for UGU District Municipality, engineered by Royal Haskoning DHV. The appointment was a completion contract — we were brought in to finish an upgrade already under way.
Completion contracts are their own discipline. You inherit someone else's setting-out, someone else's reinforcement, and often incomplete records of what was actually cast. Before pricing any of the remaining work, the first task is establishing what is genuinely there and what has to be opened up and verified.
Building Around a Live Plant
The hardest part of a treatment works upgrade is usually not any individual structure. It is sequencing the works so the town keeps receiving water.
That drives decisions a greenfield project never faces. Temporary bypasses have to be designed and built. Tie-ins get scheduled for low-demand periods. Shutdowns are measured in hours and negotiated with the operator well in advance. A structure that could be poured in one continuous operation on an open site may instead be built in sections, because half the plant has to stay in service.
It is also why filter refurbishment reads as a small contract but behaves like a demanding one. Replacing monolithic filter floors, nozzles and media — as we did at the Kloof and Kokstad filter beds — means taking filters out of service one at a time, working to a fixed handback date, and getting the nozzle setting-out right, because a poorly laid floor shows up as uneven backwash across the bed for the rest of its life.
What to Look For in a Contractor
If you are specifying this work, three things are worth probing beyond price:
- Liquid-retaining experience specifically. Water-retaining concrete is a different discipline from general structural concrete — mix design, crack-width control, joint detailing and waterproofing all differ. A contractor's building portfolio does not tell you whether they can hold water.
- Mechanical and electrical coordination. A treatment works is a process plant. At Ethembeni we carried out the full mechanical and electrical installation, including pumps and controls, alongside the concrete works. Where the M&E sits in the contract structure determines who owns the interfaces.
- Evidence of working around live operations. Ask directly how previous shutdowns were sequenced and what the actual handback durations were.
Our Record in This Field
Water treatment and bulk water form the largest part of our portfolio — 42 of the 92 projects in our database. Among the treatment works specifically: Bhobhoyi, Makhabeleni, Ethembeni, Mtwalume and Ndelu, the Howick filter unit for Umgeni Water, and filter bed replacements at Kloof and Kokstad. Several were repeat appointments from the same municipality, which we regard as the more meaningful indicator.
If you are planning a treatment works upgrade and want to discuss sequencing or constructability before it goes to tender, that conversation is usually most useful early.