Borehole Rehabilitation & Flushing in Kenya: Restore Lost Yield

What is Borehole Rehabilitation?

Hiring the wrong contractor for borehole rehabilitation could waste your money and leave your water supply worse than before. Before you commit, verify that the company holds a valid Water Resources Authority (WRA) license and has a proven track record in borehole restoration. This guide explains everything you need to know about borehole flushing and yield recovery in Kenya.

Borehole rehabilitation is the process of restoring a borehole's lost or declining water yield. Over time, boreholes naturally accumulate sediment, mineral scale, and biological growth that clog the screen and reduce water flow. Professional rehabilitation uses specialized mechanical, chemical, and hydraulic methods to clean the borehole and restore its original performance.

At WaterLink Limited, a WRA licensed borehole drilling company with Class A status, we've rehabilitated over 120 boreholes across Kenya, restoring yields by up to 90%. This guide explains why rehabilitation is often far more cost-effective than drilling a new borehole.

Why Do Boreholes Lose Yield?

Several factors can cause a borehole to lose yield over time:

1. Screen Clogging

The borehole screen allows water to enter while keeping sand and sediment out. Over time, the screen slots can become clogged with mineral scale, iron bacteria, or fine sediment.

2. Biofouling (Bacterial Growth)

Iron bacteria and other microorganisms thrive in borehole environments. They produce slimy biofilms that clog screens and reduce flow. This is particularly common in areas with high iron content in the water.

3. Mineral Scale Buildup

Calcium carbonate and other minerals precipitate out of the water and form hard scale on the screen and pump components. This is more common in boreholes with hard water.

4. Sediment Accumulation

Fine sand and silt can settle in the bottom of the borehole, reducing the effective depth and water storage capacity.

5. Dropping Water Table

Regional groundwater levels can drop due to over-extraction or drought. The borehole may not be deep enough to reach the new water level.

6. Pump Wear

Sometimes the pump itself is the problem. Worn impellers or damaged valves reduce pumping efficiency.

7. Casing Damage

Collapsed or perforated casing allows sediment to enter the borehole, clogging the screen.

Signs Your Borehole Needs Rehabilitation

Watch for these warning signs:

• Decreased Water Flow: Taps running slower, longer fill times for tanks.
• Pump Runs Longer: Pump cycles more frequently or runs continuously.
• Rising Electricity Bills: Pump works harder to deliver the same water.
• Sediment in Water: Sandy or muddy water from taps.
• Unusual Odors: Musty or sulfur-like smells (iron bacteria).
• Discolored Water: Reddish or brownish water (iron or manganese).
• Lower Pressure: Significantly reduced water pressure.
• Declining Water Level: Lower static water level measured in the borehole.

Borehole Rehabilitation Methods

WaterLink Limited uses a range of rehabilitation methods, depending on the specific problem:

1. Mechanical Cleaning

Method: Brushing, surging, and high-pressure jetting to physically remove deposits from the screen and borehole walls.

• Best For: Sediment accumulation, light scale buildup.
• Effectiveness: 60-80% yield recovery.

2. Chemical Treatment

Method: Acidization to dissolve mineral scale (calcium carbonate, iron oxide) and disinfectants to kill bacteria.

• Best For: Mineral scale, iron bacteria, biofouling.
• Effectiveness: 70-90% yield recovery.

3. Hydrofracturing

Method: High-pressure water is injected to open new fractures in the surrounding rock, increasing water flow into the borehole.

• Best For: Low yield due to poor fracture connections.
• Effectiveness: 50-200% increase in yield.

4. Air Lifting / Surge Block

Method: Compressed air is used to create powerful surges that flush debris from the screen and surrounding formation.

• Best For: Sediment and light clogging.
• Effectiveness: 50-70% yield recovery.

5. CCTV Inspection

Method: A downhole camera identifies the exact cause of the problem before any work begins.

• Best For: All cases (diagnostic first step).
• Effectiveness: Identifies the problem accurately.

6. Casing Repair / Liner Installation

Method: Installing a smaller diameter liner inside the existing casing to bypass damage.

• Best For: Collapsed or perforated casing.
• Effectiveness: Restores structural integrity.

Rehabilitation Methods at a Glance

The Rehabilitation Process Step-by-Step

Here's how WaterLink Limited approaches borehole rehabilitation:

Step 1: CCTV Inspection

We lower a high-definition camera into the borehole to identify the exact cause of the problem. This avoids guesswork and ensures the right treatment.

Step 2: Pump Removal

If necessary, we safely remove the pump and drop pipe to access the borehole.

Step 3: Initial Flushing

We use air lifting or surging to remove loose sediment and debris.

Step 4: Chemical Treatment (if needed)

We apply the appropriate chemicals to dissolve scale or eliminate bacteria. The solution is left to work for the required time.

Step 5: Mechanical Cleaning

We use brushes, jetting tools, or other mechanical methods to physically clean the screen and borehole walls.

Step 6: Hydrofracturing (if needed)

If fractures are the problem, we isolate the zone and inject high-pressure water to open new flow paths.

Step 7: Final Flushing and Development

We thoroughly flush the borehole to remove all debris and treatment chemicals.

Step 8: Yield Testing

We conduct a new yield test to measure the improvement and confirm the rehabilitation was successful.

Step 9: Pump Reinstallation

We reinstall the pump and test the complete system.

Cost of Borehole Rehabilitation in Kenya

The cost of borehole rehabilitation varies based on the depth, method required, and severity of the problem:

Note: Costs vary based on borehole depth, accessibility, and specific conditions. WaterLink Limited provides a detailed quote after a CCTV inspection.

When to Rehabilitate vs. Drill a New Borehole

Deciding between rehabilitation and new drilling depends on several factors:

When Rehabilitation is the Best Option

• Yield loss is gradual and not structural – Clogging, scaling, or biofouling.
• Water quality is still acceptable – No contamination or salinization.
• Casing is in good condition – No major damage or collapse.
• Budget is limited – Rehabilitation is much cheaper.

When Drilling a New Borehole is Better

• Casing is completely collapsed – Cannot be repaired.
• Water quality has deteriorated permanently – Salinization or contamination.
• The water table has dropped significantly – The borehole is no longer deep enough.
• Multiple rehabilitation attempts have failed – The borehole has reached the end of its life.

Preventing Future Yield Loss

After rehabilitation, regular maintenance prevents future problems:

• Annual Inspections: Regular CCTV inspections catch problems early.
• Water Quality Testing: Monitor for changes in chemistry that could cause scaling.
• Pump Performance Monitoring: Track flow rate and electricity consumption.
• Maintenance Contracts: Professional maintenance plans keep your borehole in top condition.
• Abstraction Management: Don't exceed the sustainable yield of your borehole.