IPA: /ˈreɪnˌwɔːtə/
KK: /ˈreɪnˌwɔːtər/
Water that falls from the sky as rain and is usually clean and soft, containing few minerals.
We collected rainwater to use for watering the garden.
Rainwater → It is formed from "rain" (from Old English *regn*, meaning water that falls from the sky) and "water" (from Old English *wæter*, meaning liquid that falls as rain). The word "rainwater" refers to the water that falls as rain.
Think of 'rain' as the water that falls from the sky and 'water' as the liquid itself — together, they describe the water that comes from rain.