The hydrological cycle is also known as the water cycle.
The water is recycled again and again through the process of evaporation, condensation and water transfers such as surface run-off.
Step 1 Evaporation- Water changes to a gas and evaporates to the air.
Step 2 Condensation: Water condenses into clouds.
Step 3 Precipitation- Water falls from the clouds as rain, snow, sleet or hail.
Step 4 Surface runoff- Water goes to lakes, river, oceans or Aquifers(underground rivers- percolation)
Step 5 Transpiration- Some water gets absorbed by the plants for photosynthesis and evaporates in the plants.
Hard water is water that contains an appreciable quantity of dissolved minerals (like calcium and magnesium). Calcium hydrogen carbonate is the main cause of hard water. It forms when rain falls on rock of limestone and chalk. These are made of calcium carbonate which is not soluble in water. But rainwater contains CO2 disolved from the air, which makes it acidic. So it reacts with the rocks to form calcium hydrogen carbonate which is soluble an ends up in taps. The reaction is:
H2O + CO2 + CaCO3 ---> Ca(HCO3)2
2 types of hardness:
- Temporary- Hardness can be removed.