When I started out cross stitching I was really disappointed by the limited selection of Aida cloth colors available. I love that embroidery can be done on so many different fabrics, so I was really excited to find out about water soluble canvas. It is a plastic sheet with holes for cross stitching that dissolves away when put in water and allows you to cross stitch on any fabric!
When cross stitching with the water soluble canvas, first start by basting down the canvas to the fabric. For some really small projects I have skipped this step, but it is pretty important if you're doing a larger design because you want to keep the canvas in place and prevent it from shifting around.
Stitching the design is just like if you were using Aida cloth, except you will need a slightly sharper needle. I usually use tapestry needles for cross stitch since the holes are already in the fabric, but when using water soluble canvas I do use an embroidery needle.
Now this step isn't completely necessary, but before I start soaking off the canvas I like to go and trim away any larger excess pieces. The water soluble canvas is a bit pricey and so I like to save all the little scraps and use them later for smaller projects. However, do this very carefully because I accidentally stabbed a little hole in the fabric trying to get the canvas out from the interior piece!
Fill a large bowl or container with water water and a tiny bit of dishwashing soap and let it soak. The instructions on the package say to soak it for 5-10 minutes but I have found this isn't enough. After 10 minutes I rinse the fabric and if it still feels gummy or sticky, I start over with fresh hot water. The canvas does dissolve away after that first soak, but if you don't repeat it then you probably will find that when it dries the thread is stiff and rough to touch. This might not be a big issue if you plan on displaying it on the wall, but you wouldn't want this if you cross stitch on clothing.
I always rinse it one final time and wring out as much water as I can before letting it dry on a towel. Once it's dried you can press and finish it as you would any cross stitch project!