Grey water is reusable waste water from residential, commercial and industrial, bathroom sinks, bath tub, shower drains and washing of clothes.

Any feature of an organism or its part that enables it to exist under conditions of its habitat is called adaptation.

i) Biotic or living factors which include plants, animals and all other living organisms.
ii) Abiotic or Non-living factors which includes temperature, pressure, water, soil, air and sunlight.

Water recycling is reusing treated wastewater for beneficial purposes such as agricultural and landscape irrigation, industrial processes, flushing in toilets and ground water recharge.
Conventional waste water treatment involves the following stages:
Primary treatment:
Primary treatment involves temporary holding of the wastewater in a tank. The heavy solids get settled at the bottom while oil, grease and lighter solids float over the surface. The settled and floating materials are removed. The remaining liquid may be sent for secondary treatment.
Secondary treatment:
Secondary treatment is used to remove the biodegradable dissolved organic matter. This is performed in the presence of oxygen by aerobic microorganisms. The microorganisms must be separated from treated water waste by sedimentation.
After separating the sediments of biological solids, the remaining liquid is discharged for tertiary treatment.
Tertiary treatment:
It involves removal of inorganic constituents such as nitrogen, phosphorus and microorganisms. The fine colloidal particles in the sewage water are precipitated by adding chemical coagulants like alum or ferric sulphate.

The water cycle involves a series of inter connected pathways involving both the biotic and abiotic components of the biosphere.
Water continuously moves between living organisms, such as plants and non-living things such as clouds, rivers and oceans.
The steps involved in the water cycle are as follows,
1. Evaporation:
Water evaporates from the surface of the earth and water bodies such as the oceans, seas, lakes, ponds and rivers turn into water vapour.
2. Sublimation:
Ice sheets and ice caps from north and south poles and ice caps on mountains, get converted into water vapour directly, without converting into liquid.
3. Transpiration:
It is the process by which plants release water vapour into the atmosphere through stomata in leaves and stems.
4. Condensation:
At higher altitudes, the temperature is low the water vapour present there condenses to form very tiny particles of water droplets. These particles come close together to form clouds and fog.
5. Precipitation:
Due to change in wind or temperature, clouds combine to make bigger droplets, and pour down as precipitation (rain). It includes drizzle, rain, snow and hail.
6. Run off:
As the water pours down, it runs over the surface of earth. Runoff water combines to form channels, rivers, lakes and ends up into seas and oceans.
7.Infiltration:
Some of the precipitated water moves deep into the soil, then it moves down and increases the ground water level.
8. Percolation:
Some of the precipitated water flows through soil and porous or fractured rock.