Sustainable Services

Rainwater Harvesting

A Sustainable Water Management Solution to Counter Water Scarcity.

Rainwater harvesting systems collect and store rainwater for human use — ranging from simple rain barrels to elaborate structures with pumps, tanks, and purification systems. Collected rainwater can be used for laundry, house cleaning, irrigation, fire extinguishing, toilet flushes, or car wash.

Collecting and storing rainwater with zero emissions increases available water resources, reduces city floods and pollution, and improves urban water management. It also reduces the amount of piping needed for water networks and mitigates the adverse environmental effects of urban life.

Rainwater Harvesting

Types of Rainwater Harvesting Systems

Active Rainwater Harvesting — Rainwater is stored in above-ground or underground cisterns, ponds, or other receptacles for later use — for irrigation, fountains, animals, and domestic purposes.
Passive Rainwater Harvesting — Rainwater is stored on-site where it falls and infiltrated into the ground for landscape and groundwater recharge. No storage tanks required. Soakaway pits are constructed to direct water into the groundwater system.

Components of a Rainwater Harvesting System

A good system is divided into four main subsystems — Collection, Treatment, Storage, and Distribution.

1. Collection

Gutters — Collect water that falls on the roof and channel it to the storage tank. Common materials include PVC, vinyl, seamless aluminum, and galvanized steel. Gutters should be at least 5 inches wide to handle a 100-year storm event.
Downspouts — Direct water from gutters to storage. Properly sized downspouts ensure water flows without collecting unneeded debris.
Leaf Filter — Installed along gutters, in downspouts, and at the storage tank entrance to remove leaves and debris before water enters the system.
First Flush Diverter — A valve that diverts the first spell of rain — which contains the most pollutants from the air and roof — away from the storage tank.

2. Treatment

Sand Gravel Filter — Constructed with brick masonry filled with layers of pebbles, gravel, and sand, each separated by wire mesh. Removes silt, dust, leaves, and organic matter.
Charcoal Filter — Layers of pebbles, gravel, sand, and charcoal in a drum or chamber. The thin charcoal layer absorbs odor. Each layer separated by wire mesh.
PVC Pipe Filter — A 1–1.2m PVC pipe divided into compartments filled with gravel and sand alternately. A 6" pipe covers up to 1500 sq ft roof; 8" for larger roofs. Can be installed horizontally or vertically.
Overflow Treatment — When the storage tank is full, overflow water is treated through a natural sand, gravel, and rubble bed filter in a separate trench to allow percolation to groundwater.

3. Storage

The storage tank is designed according to water requirements, rainfall, and catchment availability. Each drainpipe should have a mesh filter, first flush device, and filtration system before connecting to the tank. Each tank must have an overflow system directing excess water to the recharge system. Water from storage tanks can be used for washing, gardening, and other secondary purposes.

4. Distribution

Water from the storage tank is distributed to toilets, washbasins, and irrigation points depending on water quality. Distribution includes all piping, pumps, and devices that move water from storage to point of use. For drip irrigation by gravity, a simple length of drip tubing may suffice. For indoor pressurized use, a licensed plumber should handle installation and ensure compliance with local backflow prevention requirements.

Resources

Methods of Rainwater Harvesting — Article (PDF) How to Recharge Underground Water — YouTube Video Rainwater Harvesting Whitepaper — Download PDF