Praise be to Allaah.
It is permissible to use tissue paper and the like for istijmaar (cleaning the private parts after passing urine or stools by using stones, paper, etc.), and that is good enough as long as they clean the area properly. It is preferable if what is used for this purpose is an odd number, such as three sheets of tissue paper, or three stones, and so on, and one should not wipe less than three times. After that it is not essential to use water, but it is sunnah to do so.
Sheikh Muhammed Salih Al-Munajjid