Rain Water that has fallen directly from the sky and collected in a glass or cup or other clean container is very safe to drink.
The rain water is usually pretty clean and is likely cleaner than your city water that you get from the tap and it doesn't contain all those chemicals such as chlorine.
I've put glasses out on a table outside and let it collect rain water and it's very refreshing to drink the rain water and I've been doing it for years.
I also used to stick my tongue out as a kid and catch the rain drops on my tongue and I'm still here today.
Rain water is the same water we drink out of our taps except it just falls from the sky and doesn't go through a treatment process.
The rain water is very clean and okay and safe to drink so if you want to drink some rain water go ahead and drink it as long as it's in a clean container.