?? 1. Where Does Water Come From?
Water is one of the most essential substances on Earth. All living things need water to survive. Let us
understand where this water comes from and how it moves around our planet.
Sources of Water:
- Rain water � the most important source; replenishes all other sources
- Rivers and streams � fed by rainwater and melting snow from mountains
- Lakes and ponds � still/standing water bodies fed by rain
- Groundwater � water stored underground in aquifers; accessed through wells and tube
wells (borewells)
- Springs � groundwater emerging naturally at the surface
- Glaciers and snowfields � frozen water in mountains; melt in summer to feed rivers
- Oceans and seas � the largest store of water, but it is salty
?? 2. The Water Cycle � Nature's Water Recycling System
The water on Earth is constantly moving in a continuous cycle called the water
cycle (or hydrological cycle). Nature never makes new water � the same water has been cycling on
Earth for billions of years!
Steps of the Water Cycle:
- Evaporation: Heat from the Sun causes water in oceans, lakes, rivers to evaporate ?
water vapour rises into the atmosphere
- Transpiration: Plants release water vapour through their stomata ? adds more vapour
to the atmosphere
- Condensation: As water vapour rises, it cools at higher altitudes ? condenses into
tiny droplets ? forms clouds
- Precipitation: When water droplets in clouds become heavy enough, they fall back to
Earth as rain, snow, sleet, or hail
- Collection / Runoff: Water collects in oceans, rivers, lakes, or seeps into the
ground ? cycle begins again
?? Image Prompt
A detailed educational diagram of the complete water cycle: Blue ocean/lake on the
left with upward-pointing arrows labeled "Evaporation (Sun causes water to rise as vapour)". Mountains
in the center-right with snowcap at top. Dark blue clouds at the top with droplets labeled "Condensation
(vapour ? water droplets ? cloud)". Downward arrows from cloud labeled "Precipitation (Rain, Snow,
Hail)". Arrows on mountain slopes labeled "Surface Runoff" leading to rivers. Underground cross-section
showing groundwater infiltration labeled "Groundwater Infiltration". Circular arrows connecting all
parts. Sun shown prominently on top right. Blue and green color scheme, clear educational labels,
illustrated landscape style.
Fig. 14.1 � The Water Cycle (Hydrological Cycle)
??? 3. Rainfall and Its Measurement
- Rainfall is measured using an instrument called a rain gauge
- Rainfall is measured in millimetres (mm) � the height of water collected in the
gauge
- Areas with high rainfall are tropical rainforests, coastal regions (e.g.,
Cherrapunji, Meghalaya � one of the wettest places on Earth with ~11,000 mm/year!)
- Areas with very low rainfall are deserts (e.g., Rajasthan receives barely 100-300
mm/year)
?? 4. Clouds � How Are They Formed?
Water vapour rises from the surface ? as it goes higher, the temperature drops ? vapour cools and
condenses around tiny dust particles ? forms millions of tiny water droplets ? these
together form a cloud.
When cloud droplets collide and merge, they get heavier and eventually fall as rain. If
it's very cold, they fall as snow, sleet, or hail.
?? 5. Importance of Water Conservation
Although Earth's surface is 71% water, only about 3% is freshwater, and most of that (2%) is
frozen in glaciers and ice caps! Only 1% is available as usable freshwater for drinking,
farming, and industry.
Why save water?
- Freshwater is scarce � only 1% of Earth's water is usable
- Growing population = more water demand
- Pollution is contaminating many freshwater sources
- Groundwater is being used faster than it is being replenished (overexploitation)
Ways to Conserve Water:
- Close taps when not in use (while brushing teeth, soaping hands)
- Fix leaking taps immediately � a dripping tap wastes hundreds of litres per day!
- Rainwater harvesting � collecting and storing rainwater for later use (in tanks, in
the ground)
- Drip irrigation instead of flood irrigation in agriculture
- Reuse water � water used for washing vegetables can water plants
- Plant trees � trees increase groundwater recharge and rainfall
- Avoid contaminating water bodies by not dumping garbage/chemicals
??? 6. Groundwater and Water Table
- Rainwater that seeps into the soil percolates (filters down) through layers of soil and rock
- It collects in porous underground rock layers called aquifers
- The level of stored groundwater underground is called the water table
- If groundwater is overused (too many tube wells), the water table goes DOWN ? wells dry up
- If forests are cut and rain has nowhere to soak in, less groundwater recharge happens ?
desertification
Forests absorb rainwater slowly and let it seep underground, recharging the water table.
When forests are cut down, rainwater runs off quickly into rivers (causing floods!) without recharging
groundwater. This is why deforestation causes both floods AND droughts!
?? 7. Quick Revision
- Water cycle: Evaporation ? Condensation ? Precipitation ? Collection ? Evaporation
(repeat)
- Sun is the driving energy for the water cycle
- Rainfall measured by rain gauge in mm. Wettest place on Earth =
Mawsynram/Cherrapunji, Meghalaya
- Only ~3% of Earth's water is freshwater; only ~1% usable for humans
- Groundwater = water stored underground in aquifers; accessed through
wells/borewells
- Water table = level of groundwater underground; drops if overused
- Rainwater harvesting = collecting rainwater in tanks/ponds to replenish groundwater
- Trees ? slow water runoff ? increase groundwater recharge ? keep water table high
- Conserve water: close taps, fix leaks, drip irrigation, rainwater harvesting
