is this tarp waterproof?
That's what I hear, for the $ it's worth it.
Yes, it is waterproof. And water will accumulate on it if the tarp is not well stretched and inclined.
It never rained, so I don't know.
As with any tent, it is as waterproof as you let it be (i.e. how you sit it up). We used it in a rather good rainfall and our only issue was the blowing rain that we had to readjust and block out the rain coming in the sides. We had gusts of wind that night over 50 MPH and our stakeouts didn't hold very well (we were in some rocky area, so our stakeouts were limited so to speak). Anyway, the tarp came down that night and as a result we ended up with a small tear where the pole grommet is at. I do not fault the manufacture of the tarp, just the circumstances and it is still quite serviceable. We have had it repaired (about $10 for the repair) and it has worked fine since then. I use these for boy scout backpacking trips and will probably buy a few more. The quality for the price is just too good to pass up.