Water causes refraction of light.
Rainbows are formed when sunlight is refracted through raindrops.
Rainbows are formed when light passes through water.
How are rainbows formed?

a: photosynthesis
b: Light passing through water
c: Cold air mixing with water
d: Hot air passing through water
e: Evaporation of water
f: focusing a lens
g: photosyntehsis
h: Water passing through light