Depends on the RO system. There is a medical grade that will do the trick but takes a bit more pressure to push the water through. What I don;t like about either is the water is dead and still retains the imprint of all the toxins. Water is a recording media so one must not only get rid of the "physical" toxins but erase the memory of those toxins as well. Think homeopathy. ;-)
Then you can rebuild the water by adding plant minerals back and then creating a new spin angle to cluster the water so it is more soluble.