Why Boreholes Dry Up

Few things alarm a borehole owner more than a pump that starts delivering less water, sputtering air or nothing at all. The instinctive conclusion is often, “The borehole has dried up.” Sometimes that is true. Often, however, the problem lies elsewhere: a failed pump, a blocked screen, a power problem or a temporarily lowered water level.

Correctly diagnosing the cause matters, because the remedy differs completely. This article explains the main reasons boreholes lose yield or appear to dry up, how to tell them apart and how to prevent them. It draws on hydrogeological principles that apply across Kenya, from the volcanic aquifers of Nairobi and Nakuru to the basement rocks of Machakos and the sedimentary basins of the north.

First, What “Drying Up” Really Means

A borehole is a narrow shaft that intersects an aquifer. Water flows from the aquifer into the borehole, and the pump lifts it to the surface. A borehole “dries up” when one of these links fails:

1. The aquifer no longer supplies enough water to the borehole because water levels have fallen below the productive zone or the aquifer is depleted.
2. The borehole itself has become clogged or damaged, restricting inflow.
3. The pump or its power supply has failed, so water is present but is not being lifted.
4. The pump intake is above the water level because the pumping level has dropped below the pump.

Only the first is a true depletion of groundwater. The others are mechanical or hydraulic problems that can often be fixed.

Natural Causes of Declining Yield

1. Seasonal and multi-year rainfall variation. Groundwater is recharged by rainfall and river infiltration. In years of poor rainfall, recharge declines and water levels fall. Kenya experiences droughts and the El Niño and La Niña cycles that affect rainfall. Shallow aquifers respond quickly to seasonal changes, while deep aquifers respond more slowly. A borehole that is marginal in a wet year may fail during a prolonged drought.

2. Limited aquifer storage and recharge. In many hard-rock settings, groundwater is stored in fractures and weathered zones that hold limited volume. A borehole in such an aquifer may yield well at first by draining stored water, then decline as the stored volume is depleted and recharge cannot keep pace. This is especially common in arid and semi-arid areas, where recharge is small.

3. Intersecting a small or isolated fracture. If a borehole taps a narrow fracture connected to a small volume of water, it can deliver high initial yield and then fade. A pumping test, particularly one that runs long enough to reveal boundary effects, helps detect this risk. See our pumping test article.

4. Climate change and land-use change. Changing rainfall patterns, increased evaporation and reduced infiltration due to deforestation, soil degradation and urbanisation can reduce recharge. In Kenya’s water towers such as the Mau and Mount Kenya, forest loss can affect downstream groundwater and surface water over time.

5. Natural aquifer depletion in the long term. Some deep or ancient aquifers receive little modern recharge. Pumping from them is like mining a resource. Levels decline steadily as water is removed.

Human-Caused Factors

1. Over-pumping of the borehole. Pumping above the safe yield draws water levels down, may expose screens, causes the pump to suck air and accelerates clogging. Using a pump larger than the tested yield supports is a common mistake.

2. Competition from neighbouring boreholes. In densely developed areas such as parts of Nairobi, Kiambu and Nakuru, many boreholes tap the same aquifer. Their cones of depression overlap, causing well interference and regional water level decline. A borehole that worked well in the past can struggle as new boreholes appear nearby.

3. Large-scale abstraction for irrigation, industry or water vending. Commercial pumping can significantly lower water levels over a wide area, affecting domestic boreholes and springs.

4. Reduced recharge from land development. Paving, roofing and compacted ground reduce infiltration. Rainwater that once soaked into the soil may run off into drains.

5. Poor borehole design and construction. Inadequate screen length, incorrect screen placement, poor gravel pack, insufficient development, or drilling into the wrong horizon all reduce performance and long-term yield.

6. Lack of maintenance and monitoring. Without monitoring, gradual declines go unnoticed until failure.

Mechanical and Hydraulic Causes That Look Like “Drying Up”

1. Screen clogging and encrustation. Over time, minerals such as calcium carbonate or iron and manganese oxides can precipitate on screens and in the gravel pack, especially in hard or iron-rich water. Biological growth (iron bacteria) can also cause biofouling. Fine sediments can clog openings. The result is reduced inflow, increased drawdown and falling yield even though the aquifer holds plenty of water. Rehabilitation can often restore performance (see our rehabilitation article).

2. Sand pumping and borehole collapse. Improper screen slot size or gravel pack allows fine sand to enter, abrading the pump and filling the borehole bottom. Eventually, parts of the borehole can collapse, particularly in unconsolidated formations.

3. Pump failure and wear. Pumps wear out. Worn impellers, damaged motors, burnt windings or leaking rising mains reduce output. Electrical faults, voltage problems and solar controller faults also reduce flow.

4. Water level below the pump intake. If the pumping level drops below the pump, the pump runs dry and delivers air. This may be temporary, caused by seasonal decline, or permanent if the aquifer is declining. Lowering the pump may fix it, if the borehole depth allows.

5. Air locks, leaks and valve failures. Leaks in the rising main, faulty non-return valves or blocked pipes can reduce delivery without any aquifer problem.

6. Silt, sand or debris accumulating in the borehole bottom. When the sump fills, the lower screens can be buried and the pump intake can clog.

How to Diagnose What Went Wrong

A systematic approach saves money:

Step 1: Check the power and electrical system. Confirm voltage, fuses, controller function and cable integrity. For solar systems, check panels and controller.

Step 2: Check the surface plumbing. Look for leaks, closed valves, blocked pipes or tank problems.

Step 3: Measure the water level in the borehole with a dip meter. Compare it with the pump depth and with the original static water level recorded when the borehole was completed.

Step 4: Compare current yield with test pumping records. Measure the flow rate with a meter or bucket test and compare with the earlier yield.

Step 5: Inspect the pump. Pulling the pump allows inspection of wear, scaling, damage and cables. Many “dry borehole” problems turn out to be pump issues.

Step 6: Check the borehole depth and condition. A downhole camera or caliper survey, where available, can reveal casing damage, screen blockage, sediment fill and total depth. Compare total depth against the original completion report.

Step 7: Test water quality and conductivity. Changes can indicate changing aquifer conditions.

Step 8: Review monitoring data and neighbours’ activity. Look for new boreholes, large abstractions or seasonal patterns.

If the static level is still high and the borehole is deep and clean, but flow is poor, suspect pump or plumbing. If the static level has fallen below the productive zone, suspect aquifer decline or interference. If the static level is normal but drawdown is much larger than before, suspect clogging.

Prevention: Before and During Construction

1. Commission a proper hydrogeological survey to site the borehole in a favourable setting and estimate sustainable yield.
2. Design the borehole for the aquifer. Choose the right diameter, screen type, slot size, gravel pack and screen position for the formation.
3. Ensure proper development to remove drilling fluids and fine particles from around the screen.
4. Do a thorough pumping test to determine safe yield and drawdown behaviour.
5. Use a licensed contractor and supervise construction.
6. Install a sanitary seal and protective headworks to prevent contamination and sediment entry.

Prevention: Operation and Management

1. Pump within the safe yield. Do not exceed the recommended rate. Use storage tanks so you can pump at a moderate rate for longer rather than at a high rate for short periods.
2. Install a water meter and keep a log of abstraction.
3. Monitor water levels regularly with a dip meter or logger. A steady decline is an early warning.
4. Install protection devices such as dry-run protection or low-level cut-offs to prevent pump damage when levels drop.
5. Set the pump at an appropriate depth with margin for seasonal drawdown.
6. Service the pump and system regularly, including inspecting the pump, rising main and electrical equipment according to manufacturer guidance.
7. Manage water quality risks such as scaling and iron bacteria through monitoring and, where needed, preventive treatment.
8. Avoid contamination sources near the borehole, such as latrines and chemical stores.

Prevention: Aquifer and Catchment Management

Improve recharge. Practices include rainwater harvesting, recharge pits and trenches, sand dams in suitable landscapes, soil and water conservation on farms, tree planting and protecting wetlands. Allowing roof runoff to infiltrate in suitable places rather than draining away supports local recharge.

Share information and coordinate. In areas with many boreholes, communities and Water Resources Users Associations (WRUAs) can work with the Water Resources Authority to monitor water levels, regulate abstraction and plan sustainably.

Respect the permit. Abstraction permits exist to keep total abstraction within sustainable limits. Complying with conditions helps protect everyone’s supply.

Plan for drought. Maintain storage, have a backup source and adopt water-saving practices. For farms, irrigation scheduling and efficient systems reduce demand.

What to Do If Your Borehole Has Dried Up

1. Do not panic or immediately re-drill. Diagnose first.
2. Switch off the pump to protect it if it is running dry.
3. Measure the water level and review records.
4. Engage a hydrogeologist and a reputable pump technician to investigate.
5. Consider rehabilitation if clogging is the cause (cleaning, acidising, surging, jetting) or pump repair or lowering.
6. Consider deepening only when the hydrogeological assessment shows deeper productive zones exist, and check with the Water Resources Authority if deepening affects permit conditions.
7. Reassess demand and operations. Reduce pumping rate or schedule pumping to allow recovery.
8. Consider alternative or supplementary sources, such as rainwater harvesting, storage or a new, well-sited borehole.

Frequently Asked Questions

Can a borehole recover after drying up? Yes, if the cause is seasonal. Water levels often recover after good rains and after pumping stops. Clogged boreholes can be rehabilitated.

How long should a borehole last? A well-sited, constructed and maintained borehole can last decades, although pumps need periodic replacement and screens may need rehabilitation.

Is deepening always the answer? No. If the problem is clogging, a failed pump or interference, deepening will not help and could waste money.

Can neighbours’ boreholes really affect mine? Yes. When two boreholes tap the same aquifer, their cones of depression can overlap and lower water levels at both.

Will treating the water prevent clogging? In some cases, yes. Managing iron, scaling and biological growth through proper design and treatment can slow clogging, but the approach depends on water chemistry.

Conclusion

Boreholes rarely “dry up” for a single obvious reason. Natural variation, aquifer limits, over-pumping, neighbouring abstraction, clogging and mechanical failures all play a part. The best protection is science-based siting, good construction, realistic pumping rates, regular monitoring and a commitment to sustaining the aquifer through recharge and responsible management.

If your borehole is losing yield or you want to plan a reliable new one, contact Reg. Geol. Mbugua Githae (MGSK) through consult.innercoregeoconsultants.co.ke for hydrogeological assessment and advice.