(C) Non-renewable (or Exhaustible) Resources: Cannot be regenerated, renewed, or replaced within a time framework.

(D) Intangible Resources: Available in huge quantities but can be easily destroyed.

(A) Biotic Resources: Originated from living organisms or have life.
- Examples:
  - Renewable: Livestock, fisheries, flora, fauna, humans.
  - Non-renewable: Coal, petroleum.
(B) Abiotic Resources: Non-living origin.
- Examples: Minerals, rocks, water.

Sources of water useful or potentially useful to humans.
Prerequisite for life (plants, animals, humans cannot survive without water).
Used in agricultural, household, industrial, recreational, and environmental activities.

Continuous movement of water above and below Earth's surface, driven by the sun.
Sun heats water in seas/oceans $\rightarrow$ Water evaporates into air as vapor.
Snow and ice can sublime directly into water vapor.
Rising air currents carry vapor into atmosphere $\rightarrow$ cooler temperatures condense to clouds.
Air currents move clouds $\rightarrow$ collide, grow, fall as precipitation.
Most water falls back to oceans or land as rain $\rightarrow$ flows as surface run-off.
Evaporation: Transformation from liquid to gaseous phase.
Sublimation: State change directly from snow/ice to water vapor.
Condensation: Transformation of water vapors to liquid water droplets (fog/clouds).
Precipitation: Condensed water vapor falling to Earth's surface as rain.
Surface run-off: Water movement across land.
Percolation: Infiltration of surface water for groundwater storage.

Total Water on Earth:
- Saline Water (oceans): 97%
- Fresh Water: 3%
  - Icecaps and Glaciers: 68.7%
  - Ground Water: 30.1%
  - Other: 0.9%
  - Surface Water: 0.3%
    - Lakes: 87%
    - Swamps: 11%
    - Rivers: 2%

Growing population & better lifestyles $\rightarrow$ increased per capita fresh water use $\rightarrow$ shortage.
Spatial & temporal variations in available water.
Freshwater resources reduced by pollution.
Extreme weather conditions (floods, droughts, typhoons, cyclones) $\rightarrow$ worsening water quality & availability.