Hint: The answer here is very much related to the usage of water now-a-days. We can just think how we use water these days and write the related answer. Here the term mismanagement means how badly or unorganised the process is.
Complete answer: To understand the mismanagement of water, we must first understand the management of water and steps for managing water correctly. Management of water means planning and developing the optimal ways to use water. As we all know water is important for everyone’s life and, of all the water present on the earth, only three percent is usable(fresh) and two-thirds of this freshwater is in glaciers and ice caps, and most of the remaining freshwater is at places, where we can’t go. Agriculture, which is the most important thing for humans, is the largest user of the world’s freshwater consuming around 70 percent. So, we need to use the water we have wisely and we should find new ways or apply old ways in a better way to manage the water that is left. We can call this water management. Mismanagement of water can be described as not using the water we get in an optimal way, small things that we do can come under mismanagement of water, these small things can include leaving the tap open at home or anywhere else and, using excessive water while washing the vehicle or while bathing, we can think of this as something small but its effects are far too great for us to see, many parts of a country get far less water than they should be given whereas some parts of a country use far too greater than they should.
Note: Mismanagement of water might seem like a small issue now but if everyone does the same thing then, we might as well run out of usable water in the near future. The situation is getting worse day by day and this has become a critical issue.