The maintenance of a stablel environment i think
I believe this article: http://www.pasadenavilla.com/2013/05/01/mental-health-vs-emotional-healthare-they-related/ will help you with this question.
Hey!
I'm sure there's a vast amount of ways.
From the top of my head, you could: boil the water, look for cloudiness, or whiff it for odor.
Hope this helps :))
