Water stones need regular flattening to ensure the working surfafce is flat and even. A dished stone will not have an even contact with the edge result in an inconsistantly sharpened edge. While arguably the best flattening stone is diamond plates, the upfront cost is also quite significant, sometimes even cost more than the actual waterstone. For those looking for a budget rig, the Suehiro offering is a very good choice.
Grit: Coarse, for Coarse/Medium grit waterstones
Size: 206 x 54 x 27mm