The essential requirement in purification (taharet) is the removal of impurity (necaset). This can be done through any method, as long as the impurity is effectively removed. While using water is the preferred and most effective way to cleanse, as it ensures that no traces of impurity remain, alternative methods can be used when water is unavailable or when there is a specific reason preventing its use.
For example, cleaning with a wet tissue or even a dry tissue can also serve the purpose of purification. If neither of these are available, other solutions can be explored, as long as the goal is to remove the impurity.
In conclusion, the primary requirement in purification is the removal of impurity, and as long as this is achieved, the method used is acceptable.