Water Treatment Process

Water Source and Abstraction

GAWASCO draws its raw water through a surface abstraction point located next to the Garissa River Tana Bridge, along the Tana River. The abstraction system is mounted on a floating pontoon, allowing pumps to draw water reliably regardless of fluctuations in river level.

• Abstraction Point: Tana River, adjacent to the Garissa Tana Bridge
• Pump Configuration: Submersible pumps mounted on a floating pontoon
• Raw Water Conveyance: Water is pumped from the river into the Pre-Sedimentation Basin, then conveyed 3.9 km to the Treatment Plant via a DN500 epoxy-coated, cement-lined steel pipeline using surface pumps

Water Treatment Process

At the Treatment Plant, raw water undergoes full conventional treatment to ensure it meets national and international drinking water quality guidelines. The process follows a series of carefully controlled stages:

1. 01

   Pre-Sedimentation

   Raw water pumped from the Tana River abstraction point is received at the Pre-Sedimentation Basin, where heavier suspended solids and silt settle out before the water proceeds to the main treatment works.

2. 02

   Coagulation

   Polymer or Aluminium Sulphate (ALUM), minimum 16.5% strength, are dosed into the water to destabilise and bind fine suspended particles into larger, settleable flocs.

3. 03

   Flocculation

   The dosed water passes through a series of baffle walls that gently agitate the flow, encouraging the coagulated particles to collide and grow into larger flocs suitable for settling.

4. 04

   Sedimentation and Clarification

   Flocculated water flows into the sedimentation basin and clarifier, where the flocs settle out under gravity, significantly reducing turbidity before the water moves on to clarification and flows through the decanting troughs and into filtration.

5. 05

   Filtration

   Clarified water passes through decanting troughs into rapid sand filters, which remove any remaining fine particles and further polish water clarity.

6. 06

   Disinfection

   Filtered water is disinfected using High Test Hypochlorite (HTH), minimum 65–70% chlorine strength, to eliminate pathogens and ensure the water is microbiologically safe before storage.

7. 07

   Clear Water Storage

   Treated and disinfected water is collected in the clear water sump, ready for distribution to consumers across Garissa town.

Distribution Network

From the clear water sump, treated water is evacuated using various surface pumps to several strategically located, elevated steel storage tanks. From these elevated tanks, water gravitates naturally through the pipe network to reach consumers across the service area, ensuring consistent pressure and reliable supply.

Water Quality Assurance

GAWASCO maintains a rigorous water quality monitoring programme. Water samples are collected at various points along the treatment and distribution chain — from the abstraction point through to consumer taps — to verify that water quality consistently meets set national and international guidelines.

• Routine sampling at the treatment plant across all treatment stages
• Monitoring at elevated storage tanks prior to distribution
• Spot sampling within the distribution network and at consumer points
• Continuous compliance checks against national drinking water quality standards

Our Commitment

Overall, GAWASCO remains committed to providing high-quality water treatment services that are reliable, effective, and affordable. Despite the challenge of ageing equipment, its experienced team of professionals and customised solutions position it well to serve the water treatment needs of clients across various sectors within Garissa municipality.