We take Ivy swimming every week and so far we've had no problems. In fact her skin seems to benefit from the water. We cream her with her normal cream before going in the pool and then a good cream afterwards. Last summer we went to an indoor water park and spent about 2 hours in the water. I did start to panic that she had been in too long but again it didn't seem to affect her. We do put an all in one suit on her - not that I think it makes any difference but is to stop her being so slippy in the water!
Sand seems to exfoliate her skin. We've never had any problems with it either. It seems that there are differences and what works for one little one might not work for others. But I've always thought if you don't try you never know!
Good luck.

4 year old girl with Lamellar Ichthyosis

Baby girl unaffected