Whichever method you choose, be it a waterstone (also known as a whetstone), or a pull-through (either V-shaped or ceramic wheels) it's important to regularly hone your knife with a honing steel, which we'll also cover below. You'll be pleased to hear that you won't have to reach for the stones too regularly – once every two or three months should suffice. 
A good whetstone and a little practice will keep all of your knives sharp and in perfect condition. The beauty is that it doesn’t take much effort to learn, just a good bit of practice to get the angle right and keep a consistent angle while you’re sharpening. Whetstones are available in department stores or online, and while they range in price based on the fineness of the grit, this thread at eGullet can help you pick a good grit to start with.
Over the course of two days I re-sharpened nearly a dozen old blades, including removing the secondary bevel on an old stainless Ontario saber-grind Navy diver's knife, convexing the edge on flat ground 1095 Schrade 55 that also came with a secondary bevel, and fixing a broken tip on an old Kershaw folder. These stones made quick work of the Schrade and Kershaw. Both had completely new edge geometry within 30 minutes apiece. The Kershaw looked like-new, as if the tip had never broken. And the Schrade cut much better than it's secondary bevel would previously allow, regardless of how sharp I got it with a ceramic rod and strops. The Ontario took a little more work, as it had been abused a little the last time I'd held it, over 25 years ago and was as dull as a case knife - one of the reasons I decided to go ahead and do a full saber grind - well, a slightly convexed saber, I suppose would be more accurate. But within under an hour of using the two stones and a couple leather strops (one with black compound, another with green), the Ontario was shaving sharp again too.
I'm using this for a set of kitchen knives. As far as their quality goes, they are a name brand, but middle tier at best. The kind you can pick up at a mall kitchen store. They were all dull and in need of sharpening. After using these stones, my knives were all insanely sharp. They were noticably sharper than when I first bought them. I'm not experienced with sharpening stones, so I can't say how these compare with others, but for my needs as a non-professional, this set is perfect. Outperforms my needs.

As you continue to repeat strokes on the first time, eventually a tiny burr will form on the other side of the blade. To check for it, place the blade on your thumb, and pull it backwards. If the burr has formed, it should catch slightly on your thumb (with really fine grit stones, say 2000 or above, you won't feel this). This may take up to 30 or 40 strokes, and is the indication that you should switch and start sharpening the other side.
This is a hard review to write because while the stone is great and comes perfectly flat it's too darn small. My problem is I bought one of these over fifteen years ago and after a move it suffered two cracks across the face making it unusable. That stone is about 3" x 8 1/4" x 3/4" . This new version is about 2" x 7" x 1/2". It's practically impossible to polish a knife set from a big #7 plane let alone a #4 plane. I feel cramped even using it for chisels! The thickness doesn't really bother me even though my thicker stone cracked, with reasonable care I don't expect this one to crack. So although I love the actual stone I wish they still made my old stone. I guess I should have measured my original one and then compared the description but I assumed they would be the same. So because of that I took off one star but since there's nothing wrong with the actual stone I wanted to give it three stars based on the small size but couldn't.

Any stone with a flat surface was a perfect candidate for sharpening blades. A sword, however, was sharpened on a circular stone that was rotated by a handle. As you can see, knife sharpening has not undergone a huge technological shift in history. The method of sharpening has stayed consistent, while the materials improved; from flint rock to stainless steel.
If you’re sharpening high quality knives, you probably don’t want to use a cheapo sharpening stone. But if you’re just getting started with sharpening your pocket knife, there’s no need to get too fancy right off the bat. You can find a sharpening stone at most hardware stores for about $10. This one is very similar to the one I use. Nothing fancy. Most basic sharpening stones come with two sides: a rough grit and a fine grit. The finer the grit, the finer or sharper you can get your blade. You usually start off sharpening on the rough grit and then finish sharpening it on the finer grit.
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