It is from a 1956 film called "A Cry From The Streets", by Max Bygraves.
If you didn't have rain then you couldn't have showers;
If you didn't have showers then you couldn't have flowers.
There'd be no place to swim,
There'd be no babbling brook,
There'd be no fish to catch at the end of a hook.
You'd be so awfully dirty,
You'd be as black as ink,
All day you'd face the barren waste-
Looking for a nice cool drink.
So you've gotta have rain every now and then
To make the whole world shine,
Then everyday will turn out fine.
so... you're not mad after all =o)