I've been using these with my watercolor pencils (Inktense by Derwent and Aquarelle by Faber-Castell) and they are very fun. They are easy to fill up and once they are closed, they don't leak. You do have to make sure to tighten them after filling. There is a place on the barrel that says "Push" and you push gently on that area to get the water flowing. I would recommend having a separate piece of paper on the side to test that on first because it will give you a big drop of water the first time. After that, you don't have to push continually to keep the water flowing. These will give you a good amount of water so be sure to color on paper that is able to handle that or it will get wrinkled fairly quickly. The only thing I wish they had was a way to adjust how much water comes out because sometimes I only want a little bit of water. For those times, I sometimes push out a drop of water and empty the tip a bit and use that, because the brush will flow for awhile before you have to push on it again. If they could add a twist valve so you could reduce the flow of water, that would make them even better. I've seen that other people fill them with watercolor pigment, but I use them exclusively with my watercolor pencils so I only use them with plain water.