Not that one person's experience makes for anything near scientific observation, but my midwife told me before she knew I intended to birth in the water that she has had great results with women not tearing in the water. I VBACed with an 8 lb 3 oz baby and tore horribly, in both directions (3rd deg rectal & peri-urethral as well). I just gave birth two weeks ago tomorrow to a 10 lb 8 oz baby in the water [at home! yay!!] and I had one tiny superficial tear that didn't require any stitching.