Rain is a type of precipitation, a product of the condensation of atmospheric water vapor that is deposited on the Earth’s surface. It forms when separate drops of water fall to the Earth from clouds.
Rainwater is water before it hits the ground. When it hits the ground it becomes stormwater.
Rainwater it is not greywater. Greywater comes from bathroom sinks, showers and laundry.
Rainwater is much better then potable water for irrigation, because of the lack of chlorine and other chemicals used in potable water treatment. Plants thrive under irrigation with stored rainwater and may grow 20%-30% more using rainwater for irrigation.
When properly collected rainwater is valued for its purity and softness. It has a nearly neutral pH, and is free from disinfection by-products, salts, minerals, and other natural and man-made contaminants.