Check the PPM of your tap water after it rains!!!

So im never buying water from the store again.... I have well water and the ppm's are around 150-180 in the summer time. but lately it's been raining a bunch, and I usually use half RO water from the store and half tap water because RO water is kind of expensive. It's been a few days since it rained and i checked my PPM and I couldent believe my eye's. It said 18ppm. so i thought something was wrong with my meter. i re calibrated it and tested it in my hydro setup. tested a new bucket of tap water. it said 12 PPM!!!! I've tested this over the past few days and i've gotten readings between 6ppm and 18 ppm. this is great im going to save a lot of time and money running to the store. I hope this helps some of you that are still buying water.