Yes, just water for diamond stones. Wash it first with a light soap and water and maybe a 3-m pad, rinse, dry it well if you're going to store it. Most folks will feel the difference a clean diamond stone makes right away. A few drops of water now and then when sharpening, wiping with a fine cloth in between.
A sharpie marker and a magnifying glass can help you tell if you are sharpening "to the edge". If you aren't going all the way to the very edge on both sides you aren't going to get it sharp as you want. If you find you haven't taken it to the edge yet you need to remove a lot of material to get there. Use a coarser grit to "shape" the edge. I woudn't even start on the finer grits until I had flat shiny metal all the way to the edge. A waste of time trying to shape an edge with finer grits.
I use a big ol 11" stone for these and lots of room to stroke em..... IMO a VERY light circular motion works best on the 3 blade heads, catching two blade sides at a time from multiple angles. Count your stokes before rotating sides. Try to imagine only the weight of the blade on the stone for pressure.
Diamond tools don't so much "wear" out as the diamonds can be chipped and damaged with pressure, impact and heat. On most diamond tools such as concrete/stone cutting wheels the "matrix" or the material the diamonds are impregnated in is what wears and exposes new undamaged diamonds. Matching the "matrix" to the material being cut is important for those tools under power, heat, abrasion and stress. IMO a diamond stone used correctly by hand would likely last a lifetime.... or 3....
