The thing about fire is that there is not a lot you can do. Make sure there are fire alarms and fire extinguishers in the house. Otherwise, you just need to have a good insurance plan in place.
Water, on the other hand, is a different story. There are lots of different kinds of water emergencies and most of them are situations where you can do something, as the landlord.
A water emergency is a situation where things are going to get worse if the problem is not fixed as soon as possible. Most of these emergencies are bad news because they will lead to pipe damage and water damage. Your tenant can turn the water off to prevent the problem from getting worse, but you can't put off fixing the problem.
As the landlord, you are responsible for fixing the water and/or plumbing emergency. At the very least, you are responsible for calling the emergency plumber and footing the bill. This is not something you can put off because your tenant is without water until you fix the problem. You can't put this off because making your tenant go without water could turn into a serious legal issue for you.
The property that you rent must meet certain habitable standards. One of these standards requires your home to have a working toilet, a tub, hot and cold water, and a shower. As a landlord, it is your job to make sure your tenant always has access to these necessities.