In Kenya, unreliable rains and dry spells can leave your farm high and dry. Watching your crops struggle while water runs off is frustrating, especially when every drop counts for your livelihood.
This guide breaks down how to build an underground water tank, step by step. It’s a project you can manage over a few weekends, turning that wasted runoff into a reliable asset for your farm.
What You Need Before You Start
- A Site Survey: You must know your soil type and water table. Clay soil is best for lining, while sandy soil needs a liner. A local agro-vet officer or water engineer can help assess this.
- County Government Approval: For any significant excavation, you likely need a permit from your Sub-County Water Office. Fees vary by county but budget around KES 2,000-5,000.
- Clear Water Source: Decide if you’re harvesting from your roof, a road runoff, or a borehole. You’ll need gutters and pipes to channel this water to your storage site.
- Basic Construction Materials: This includes ballast, sand, cement, reinforcement wire, and a durable liner or waterproofing mixture. You can source these from local hardware shops or building material depots.
- Labour and Tools: You’ll need shovels, wheelbarrows, and a few strong hands. Hiring local fundis is a smart move for the excavation and plastering work.
Step-by-Step: How to store your farm water underground in Kenya
This process involves about six key steps and, with good planning, can be completed in two to four weeks depending on your team’s size and the weather.
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Step 1: Finalize Your Design and Get Permits
Based on your survey, decide on the tank’s size and location. Then, visit your Sub-County Water Office with your site plan to apply for an excavation permit. The fee is typically between KES 2,000 and 5,000, paid at the office.
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Step 2: Excavate the Pit
Mark the area and start digging. The shape is usually circular or rectangular. Slope the sides slightly to prevent cave-ins. This is the most labour-intensive step, so hiring a few fundis is highly recommended.
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Step 3: Prepare the Base and Walls
Compact the soil at the bottom firmly. Then, lay a 5-10 cm thick layer of concrete as the foundation slab. For the walls, you can use bricks, stones, or cast concrete, ensuring they are well-plastered on the inside.
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Step 4: Apply Waterproofing
This is the most critical step to prevent leaks. Apply a cement-based waterproofing slurry or a PVC liner meticulously over all internal surfaces. Pay extra attention to the joint between the floor and walls.
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Step 5: Install Inlet, Outlet, and Vent
Fit an inlet pipe from your water source, screened to keep out debris. Install an outlet pipe with a tap or pump connection near the base. Don’t forget a vent pipe with a mesh cover to allow air circulation and prevent vacuum.
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Step 6: Backfill and Test
Once the structure is fully cured, carefully backfill around the tank with soil. Finally, fill it partially with water and let it sit for a few days to check for any leaks before connecting it fully to your system.
Common Problems and How to Fix Them
Cracks or Leaks Appearing
This is often caused by poor curing of concrete or soil movement. The fix is to drain the tank, let it dry completely, and apply a fresh layer of a strong cement-based waterproofing sealant like ‘Sika’ or ‘Fosroc’ available at hardware stores.
Murky or Dirty Water
This usually means debris is getting in. First, ensure your inlet has a proper screen or first-flush diverter. If the water is still dirty, you may need to install a simple sand filter before the water enters the tank. Regularly clean your roof gutters too.
Low Water Pressure at the Outlet
If you’re relying on gravity, your tank might not be elevated enough. The solution is to install a small, affordable solar-powered pump. You can find good options at agro-vet shops or irrigation suppliers in major towns.
Permit Delays or Disputes
If you face long delays with your county permit, follow up politely but persistently at the Sub-County Water Office. For serious disputes, you can escalate the matter to the Water Resources Authority (WRA) regional office for guidance.
Cost and Timeline for How to store your farm water underground in Kenya
The total cost depends heavily on size, materials, and labour. The official county excavation permit is a fixed fee, but construction costs will vary. Pole, budgeting is key to avoid surprises.
| Item | Cost (KES) | Timeline |
|---|---|---|
| County Excavation Permit | 2,000 – 5,000 | 1-2 weeks |
| Materials (for a 10,000L tank) | 70,000 – 120,000 | Procurement: 1 week |
| Skilled Labour (Fundis) | 15,000 – 30,000 | Excavation & Construction: 2-3 weeks |
Hidden costs often include transporting materials to a remote farm, buying a good waterproofing liner, and the pump or piping system. Costs can be higher in remote areas due to transport. The curing and testing phase adds another 1-2 weeks before you can use the water.
The Bottom Line
Building an underground water tank is a smart, long-term investment for any Kenyan farmer facing unreliable rains. The process is straightforward, but proper planning and getting that county permit first is what makes everything else flow smoothly. With your own water reserve, you can face dry seasons with much more confidence.
If this guide was helpful, share it with a fellow farmer who could benefit. For more tips on efficient water use, check out our article on drip irrigation systems.
Frequently Asked Questions: How to store your farm water underground in Kenya
What is the cheapest way to build an underground tank?
The most cost-effective method is using a ferrocement design with locally available sand, cement, and wire mesh. This avoids expensive pre-fabricated plastic or fibreglass tanks.
However, you must invest in good waterproofing to prevent leaks, which saves money long-term.
How deep should I dig the pit?
The depth depends on your water table and desired capacity. A common depth is 1.5 to 2.5 metres for a medium-sized tank.
It’s crucial to dig deeper than the water table to avoid the tank floating or cracking during the rainy season.
Do I really need a permit from the county?
Yes, for any significant excavation, a permit from your Sub-County Water Office is legally required. It helps ensure your structure is safe and doesn’t interfere with underground utilities.
The small fee (KES 2,000-5,000) is worth avoiding potential fines or being forced to fill the hole later.
Can I do this myself or must I hire fundis?
You can manage the project yourself, but the excavation and plastering work is very labour-intensive. Hiring skilled fundis for those steps is highly recommended for a quality, lasting result.
It saves time and reduces the risk of costly mistakes like poor waterproofing.
How do I keep the water clean and safe for crops?
Always use a mesh screen on the inlet pipe to filter out leaves and debris. Installing a simple first-flush diverter is also a great idea.
For algae prevention, ensure the tank is completely covered and dark inside, and consider a vent pipe with a fine mesh.
