Green water is made with alum, lime and water. The only purpose for it is to flush any spiritual food given by herbalists which is retained within the body, or people who eat in their dreams.
Physically there are things which manifest from food given to people spiritually. So, as directed by The Holy Spirit, people are given green water to drink.
On the other hand, altar water is ordinary water, but the Holy Spirit descends and transforms it for multiple uses. Depending on the direction of The Holy Spirit. It can be used in the following ways:
1) to help those who want to have children,
2) for those who have excessive anger issues, and
3) for those looking for healing.