Rainwater Harvesting in India: A Crucial Step Towards Water Security

 

Rainwater Harvesting in India: A Crucial Step Towards Water Security

India, a country with a population of over 1.4 billion, faces significant water challenges. The unpredictability of rainfall, rising demand, and declining water tables have made rainwater harvesting a vital strategy for ensuring water security.

Challenges:

Unreliable Rainfall: India's rainfall patterns are increasingly unpredictable due to climate change, leading to droughts and floods.

Depleting Groundwater: Over-extraction has led to declining water tables, affecting agriculture, industry, and domestic supplies.

Water Scarcity: India's per-capita water availability is decreasing, threatening economic growth and food security.

Benefits of Rainwater Harvesting:

Supplements Water Supply: Harvested rainwater reduces dependence on municipal supplies and groundwater.

Replenishes Groundwater: Recharged groundwater helps maintain healthy water tables.

Flood Mitigation: Harvesting rainwater reduces stormwater runoff, minimizing flood risks.

Improved Water Quality: Harvested rainwater can be treated for non-potable uses, reducing the burden on municipal treatment plants.

Indian Context:

National Water Policy: Emphasizes rainwater harvesting as a key strategy for water conservation.

Government Initiatives: Many states offer incentives and subsidies for implementing rainwater harvesting systems.

Community Engagement: Successful examples of community-led rainwater harvesting projects demonstrate its potential.

Call to Action:

Implementing rainwater harvesting systems in India is crucial for:

Enhancing water security

Mitigating climate change impacts

Supporting sustainable development

Join the movement towards water resilience. Invest in rainwater harvesting and contribute to a secure water future for India.

Say you are living in one of the big south Indian cities where water scarcity is normal. To determine the ideal size of an underground water reservoir for harvesting rainwater and supplementing daily water needs, we'll consider several factors:

Rainfall Data:

Bengaluru East receives an average annual rainfall of around 870 mm (34.25 in). Let's assume a 6-month rainy season with approximately 145 mm (5.7 in) monthly rainfall.

Roof Catchment Area:

You mentioned 600 sq ft can be constructed, which will be the roof catchment area for rainwater harvesting.

Runoff Coefficient:

For a roof catchment, the runoff coefficient is typically around 0.8 to 0.9. This means 80-90% of the rainfall on the roof will be collected.

Water Demand:

To size the reservoir, we need to estimate daily water demand. Please provide information on:

Number of occupants

Water usage patterns (e.g., drinking, cooking, bathing, washing machines, etc.)

Assuming moderate water usage, a rough estimate for daily water demand is:

100-150 liters per person per day (LPCD) for drinking, cooking, and bathing

Additional 50-100 LPCD for washing machines, cleaning, etc.

Reservoir Sizing Calculations:

Using the above data, we can estimate the required reservoir size.

Rainwater Harvesting Potential:

For 600 sq ft roof catchment, with 80% runoff coefficient and 145 mm monthly rainfall:

Monthly rainfall collection: 600 sq ft x 0.8 x 145 mm x 0.001 = 69,600 liters (or 69.6 KL)

Daily rainfall collection: 69,600 liters / 30 days ≈ 2,320 liters per day

Reservoir Size:

Considering daily water demand and rainfall collection, let's aim to store 2-3 days of rainfall collection and daily demand.

Assuming 200-300 LPCD (moderate usage) for 4-6 occupants:

Daily demand: 800-1800 liters

Reservoir size: 2-3 days x 2,320 liters (daily rainfall collection) + 800-1800 liters (daily demand)

Recommended reservoir size: 6,000-12,000 liters (or 6-12 KL)

Practical Considerations:

Space constraints: Consider the available space for the reservoir.

Cost: Larger reservoirs are more expensive.

Maintenance: Regular cleaning and maintenance are crucial.

Suggested Reservoir Size:

Based on these calculations, a suitable underground water reservoir size would be:

8,000-10,000 liters (8-10 KL) for a moderate water usage household

12,000-15,000 liters (12-15 KL) for a larger household or higher water demand

Additional Recommendations:

Use a first flush device to divert initial rainfall runoff, carrying debris and contaminants.

Install a sedimentation chamber to remove particulate matter.

Implement a treatment system (e.g., filtration, UV) for non-potable uses.

Connect the reservoir to the daily water supply system.

Monitor and maintain the system regularly.

Sources:

Indian Rainwater Harvesting Systems Guidelines (2012)

Bengaluru Water Supply and Sewerage Board (BWSSB) guidelines

Central Ground Water Authority (CGWA) guidelines