The perfect combination of the water-repellent nature of a tarp and comfort and beauty of a tapestry that makes up a Tarpestry does not allow it to be completely water-repellent. However, it will repel the water to a point.
Lay your Tarpestry down on the damp grass and you will stay high and dry. If you lay it down in a puddle, it will eventually saturate and you will have a soggy bottom.
You can use your Tarpestry for rain protection, if you hang it at an angle so that the water can bead up and roll down. Keep in mind that if you allow the water to pool, it will eventually saturate and you must keep the water-repellent base fabric facing the rain!