Users can subscribe to tags with the purpose of receiving notifications for the following activities:
1) New ideas.
2) New comments.
Steps to follow/unfollow tags:
1) Click on the desired tag to open the idea list having that tag. For example: 'water' tag on this idea.
2) At the top right of the idea list, you will see Follow tag button. Click on this button to follow it.
3) To unfollow the tag, simply follow the first step and then click on the 'Following Tag' button which appears on the top right end of the list.