Water leaks
Let's set aside the fact that as a planet we have huge demand for clean water and during some hot summers there is actually a shortage of drinkable water.   Even if you don't care at all for that, you should take care of your water leak as soon as possible for many other reasons.   Even if a water leak is small enough to just literally be an occasional drip, those occasional drips add up to be gallons, or even hundreds of gallons at the end of the year. 
On top of that water leaks that are inside walls cause pockets of moisture which then attracts bacteria and other parasites.   Mildew and mold is the most common and can start growing inside the walls and even be undetectable.  But that mildew inside the walls will still lower your air quality in the house as it shoots spores in the air, and if your asthmatic or affected by allergies it could adversely affect yours or your loved ones health.  Mold damage also isn't covered by most homeowners insurance policies so it's something you definitely want to avoid.   Damaged cause over time by a water leak also isn't coved by homeowners insurance, so if you become aware of any water leak you should address the problem right away, or at least as soon as possible.  
Water leaks never fix themselves and have the habit of becoming worse over time.  If you suspect your toilet is leaking but want to identify where the leak is one trick is to put food coloring in the tank to track the location of the leak.   If there is water seeping from below the toilet it's probably the wax seal at the base of the toilet that needs to be replaced.