Is it safe to use the water I've collected in a rain barrel that comes off the roof? My rain barrel is new so no problem there but wondered about the possibility of toxins from the roof shingles tainting the water? The roof is over 5 years old so would think any chemicals from them would be gone by now.... The rainwater p/H is 6.8 while my tap is around 7.8. Would like to maybe switch my tanks to half rainwater & half tap water to lower the p/H a bit.