Harvesting the Sky's Bounty
Rainwater harvesting is the collection and storage of rainwater for later use. In many African regions where water access can be limited or seasonal, harvesting rainwater provides a free, sustainable water source for gardens. This fact sheet outlines simple, low-cost methods for collecting, storing, and using rainwater in home garden settings.
Materials You'll Need
- Storage containers (barrels, tanks, or other vessels)
- Gutters and downspouts (if collecting from a roof)
- Mesh screens for filtering debris
- PVC pipes or hoses for connections
- Spigot or tap for water access
- Basic tools (saw, drill, measuring tape)
- Optional: first flush diverter
Understanding Rainwater Collection Potential
Before setting up a system, it's helpful to understand how much water you can potentially collect:
Calculating Collection Potential
For every 1mm of rainfall on 1 square meter of collection surface, you can collect 1 liter of water.
Formula: Collection area (m²) × Rainfall (mm) = Water collected (liters)
Example: A 20m² roof with 25mm of rain = 500 liters of water
Rainfall Considerations
- Consider seasonal rainfall patterns in your area
- Plan storage capacity based on dry period duration
- Account for water needs of your specific garden size
Basic Rainwater Harvesting Systems
1. Simple Barrel System
The most basic and affordable option for small gardens.
Position Your Barrel
Place a barrel or container under a roof edge where water naturally flows, or beneath a downspout. Elevate it on blocks or a stand for easier access and gravity flow.
Create an Inlet
Cut a hole in the barrel lid to match your downspout or create a funnel system. Cover with mesh screen to filter out debris and prevent mosquito breeding.
Install an Overflow
Cut a hole near the top of the barrel and attach a pipe to direct excess water away from your home's foundation.
Add a Spigot
Install a tap or spigot near the bottom of the barrel for easy water access. Drill a hole and secure the spigot with washers and plumbing tape to prevent leaks.
2. Multiple Barrel System
For increased storage capacity, connect multiple barrels in series.
Position Barrels
Place barrels side by side, with the first barrel under the downspout. Ensure all barrels are at the same height.
Connect Barrels
Drill holes near the top of each barrel and connect them with short pieces of PVC pipe or hose. Seal connections with waterproof sealant.
Add Overflow and Spigots
Install an overflow pipe on the last barrel and spigots on each barrel or just the last one in the series.
3. In-Ground Storage System
For larger capacity and cooler water storage.
Dig a Pit
Excavate a pit sized for your storage container (plastic tank, concrete cistern, or ferrocement tank).
Create a Stable Base
Add a layer of sand or gravel for drainage and a level foundation.
Install the Tank
Place the tank in the pit, ensuring the inlet and outlet points are accessible.
Connect Collection System
Direct downspouts or channels to the tank inlet. Install a hand pump or gravity-fed outlet system.
Improving Water Quality
Pre-Storage Filtration
- Leaf screens: Place mesh screens over gutters and at downspout entrances
- First flush diverter: Diverts the initial flow of water (which contains most contaminants) away from storage
- Settling chamber: A small tank before the main storage where debris can settle
Storage Considerations
- Use opaque containers to prevent algae growth
- Keep containers covered to prevent debris entry and mosquito breeding
- Clean storage containers annually
- Position containers away from tree drip lines
Water Safety Tips
- Harvested rainwater is generally safe for garden use without treatment
- Do not use for drinking without proper filtration and treatment
- If collecting from a roof, consider the roofing material (avoid lead-based paints, asbestos)
- Clean gutters regularly to prevent contamination
- For edible crops, consider drip irrigation to minimize water contact with edible portions
Low-Cost Collection Alternatives
Rooftop Collection Without Gutters
- Attach plastic sheeting or tarps to roof edges to channel water
- Use bamboo halves as makeshift gutters
- Create channels with locally available materials
Surface Runoff Collection
- Create berms and swales to direct water flow
- Dig small ponds or basins in strategic locations
- Use contour trenches on sloped land
Using Harvested Rainwater Efficiently
Distribution Methods
- Gravity-fed drip irrigation: Connect low-pressure drip lines directly to elevated tanks
- Watering cans: Fill directly from spigots for targeted watering
- Ollas: Bury unglazed clay pots connected to the rainwater system for slow release
- Mulched basins: Create mulched areas around plants to maximize water retention
Conservation Practices
- Water in early morning or evening to reduce evaporation
- Use mulch extensively to retain soil moisture
- Group plants with similar water needs together
- Incorporate organic matter into soil to improve water retention
Maintenance Tips
- Clean gutters and screens before rainy seasons
- Check and repair leaks promptly
- Empty and clean storage containers annually
- Inspect and clear overflow pipes regularly
- Check mosquito prevention measures frequently during rainy seasons
