How a Small Proportion of It Accounts for Major Water Conservation in Class 10 NCERT

Understanding How a Small Proportion of It Accounts for Water Conservation

Water is essential for life, but only a small proportion of it accounts for usable freshwater resources. Although India receives significant rainfall annually, much of it is lost as runoff or evaporates. Rainwater harvesting captures this small proportion effectively to meet local water needs. Class 10 NCERT explains that conserving even a fraction of rainfall can greatly reduce water scarcity, especially in dry regions.

• Rainwater harvesting collects rain from rooftops or land surfaces.
• It stores water for drinking, irrigation, and groundwater recharge.
• This method is environmentally sustainable and cost-effective.

By focusing on harvesting a small proportion of rainfall, communities can ensure water availability throughout dry seasons, reducing reliance on large dams and groundwater extraction.

Traditional Rainwater Harvesting Techniques Across India

India has a rich tradition of harvesting rainwater adapted to its diverse ecological zones. Class 10 NCERT highlights several ancient methods:

For example, in Rajasthan, underground tanks called 'tankas' collect rooftop rainwater, providing pure 'palar pani' during dry summers. These methods show how a small proportion of rainfall was traditionally conserved to sustain communities.

Modern Revival of Rooftop Rainwater Harvesting in India

Today, rooftop rainwater harvesting is gaining renewed importance in both rural and urban India. Despite the availability of canal water in some areas, water scarcity and pollution have encouraged this revival.

• In Karnataka’s Gendathur village, nearly 200 households collect about 50,000 litres annually per household.
• Tamil Nadu is the first state to legally mandate rooftop rainwater harvesting for all buildings.
• Shillong in Meghalaya meets 15-25% of household water needs through rooftop harvesting despite heavy rainfall.

This modern approach shows how a small proportion of it accounts for significant water conservation, reducing pressure on groundwater and large dams.

Environmental and Socioeconomic Benefits of Harvesting a Small Proportion of Rainwater

Harvesting even a small proportion of rainfall offers multiple benefits:

• Environmental: Reduces soil erosion, recharges groundwater, and maintains river flow.
• Economic: Low-cost infrastructure compared to large dams, reduces water bills.
• Social: Provides reliable water supply, especially in water-scarce regions, and reduces conflicts over water.

By conserving a small proportion of rainfall, communities promote sustainable water management aligned with ecological balance and social needs.

Comparison: Large Multi-Purpose Projects vs. Small-Scale Rainwater Harvesting

Class 10 NCERT discusses both large dams and small-scale harvesting. Here’s a comparison:

While large projects supply water and electricity, a small proportion of it accounts for sustainable water conservation through simple harvesting methods.

Worked Example: Calculating Rainwater Harvested from a Rooftop

Suppose a house has a rooftop area of 100 square meters, and the annual rainfall is 800 mm (0.8 meters). To find the volume of rainwater that can be harvested:

$$\text{Volume} = \text{Roof Area} \times \text{Rainfall} \times \text{Runoff Coefficient}$$

Assuming a runoff coefficient of 0.85 (accounting for losses):

$$\text{Volume} = 100 \times 0.8 \times 0.85 = 68 \text{ cubic meters}$$

Since 1 cubic meter = 1000 litres, the house can harvest approximately 68,000 litres annually.

This example shows how a small proportion of rainfall collected from rooftops can provide substantial water for household use.