Rainwater that is collected in clean tanks directly from the sky or in clean containers or buckets is very safe to drink.
The rainwater is likely even more clean than your public water supply and does not contain any chemicals such as chlorine or fluoride which makes the rainwater the healthier choice for water.
I've drank straight rain water several times after leaving some cups out on the outdoor table outside and the rainwater tasted very good and was even healthier than my tap water.
I collect rainwater for both drinking and also watering my garden because we get a lot of rain in our area and it saves me money on my water bill.
If you think the rainwater may be a bit dirty or contaminated you can boil it to make sure it's safe but as long as the container was clean or the area you collected the rainwater was clean it's safe to drink rainwater.
You can also stick your tongue out during rain and drink the rainwater directly from the sky as well and it will not harm you.