There is absolutely nothing wrong in drinking rain water. Rain water, I stand to be corrected, it's one of the purest water we are advised to be drinkining, instead of all these packaged water we don't know their sources. If I am not mistaken, a lot of us are caught up in this habit of drinking unwholesome water that are hazardous to our health. Little did we wonder why is there so much water-related diseases out there. Yet, we don't care, we prefer to drink water that are not safe to our body instead of us to go for pure water like rain water.
Rain is ideal for us all as it remains the only water that retains all it properties after its collection such colourless, odourless and tasteless. If you look around, there are few water that possess these essential water properties.
On a cautionary note, we should be careful about the channels use for collecting rain water, as they could carry a lot of impurities which may as well render the water itself unsafe for drinking.