FWIW, ChrisL turned me on to Tools For Working Wood when they had a run of 8x1 1/2 Norton single grits in 1,4, and 8k for sale and I bought a set. If you cut those leaving one side a full 1 1/2 you'll have some handy stones. I use mine on smiling blades and warped spines to good effect.

I've never cut a waterstone length wise with a hacksaw but I've cut a Chinese 12k, a coticule and a Dalmore blue cross ways for a slurry stone and buddy .... it was work. I wouldn't have the energy or the patience to try ripping one lengthwise.... but I'm an old man. Anyhow, if you have access to a bandsaw that is the route I would take.