It is said that rubber cement can also be used for this purpose but fine detail is difficult to achieve due to the nature of the flow of the glue. Creating textures in watercolor can be a lot of fun and not too difficult to achieve. There are many common household tools that can be employed for these techniques. Cling wrap produces a very intense effect. To create this effect, place the cling wrap on a wet wash and leave to dry.
Salt is another common household product that produces texture.
As with the cling wrap, simply sprinkle the salt onto the wash of color while it is still wet. The salt will pull some of the color to it and pool around at the same time repelling the rest away. For those painters who like landscapes, wax can be an invaluable tool. Wax resists can be done many ways but probably the simplest is to take a colorless candle and rub it onto the paper before any color is added. Many watercolorists find sponges a nessitity.