Tap vs Roof-Collected water

[WillisWill]

I don't know if this is the right forum for this, but anyway...

I recently had my tap and rain-barrel water analyzed. The TDS of the tap was 70, whereas the rain barrel was 150. The hardness of the tap was 3, whereas the barrel water was 5. I had recently cleaned off my roof with both a broom and then hose before re-attaching the water barrel. I have a shingled roof, and I believe the shingles are probably 15+ years old at this point

I understand a TDS of 70 is not horrible, but certainly not ideal. I was also under the impression that rain barrel water was superior to tap (and in fact have been told as much by my local orchid nursery), especially for paphs.

My question is whether this analysis proves that my roof-collected water is not as good as my tap, or whether the analysis was too simplistic to accurately assess. For instance, might the specific identity of the solid dissolved in each source be important (calcium/sodium in the tap vs organic ions in the barrel)?

Thanks

edit - I live in central virginia, not near any major metropolitan or industrial areas

[Ray]

A starting TDS of 70 is great! It probably consists mostly of carbonates of calcium, magnesium and iron, none of which is likely to be an issue with even the most sensitive of plants at that level.

Personally, with that tap water, i wouldn't hassle with collecting the rainwater.