Besides having a shower curtain liner on the inside and keeping it tight to the corners when showering, try your local hardware store for a corner piece of rubber/plastiic made special for this problem. You just use caulking to fix it into place.
Hello, I Have A Shower Which Goes Into A Roll Top Bath. How Do I Stop Water Leaking Down The Corner And Side Of The Bath? There Are Walls Around Three Sides Of The Bath Which Leaves A Triangular Space At The Top Corner. Hope That Makes Sense! Please