A Fire Loss is Usually A Water Loss Also
Will enough water thrown into a fire put it out? In order to put out a fire with water, you need to soak the fuel.
Now, this only works on certain types of fire. Electrical fires and grease or oil fires can't be put out with water, and it's incredibly dangerous to try. Water only works when you have a solid fuel that will absorb water, such as wood, paper, cloth, etc. With those things, the main effect of the water is to lower the temperature. When water hits something of very high temperature, it boils, and by boiling it absorbs a lot of heat, rapidly cooling the fuel. When the fuel is no longer hot enough to burn, the fire goes out. Larger fires require more water to cool everything down.
A secondary effect of the water is to block the flow of air. When porous material gets soaked with water, the passages for air get blocked, so not as much air is able to get through. In situations like that, you can effectively smother a fire with water, making it impossible to burn. Between those two effects, water is one of the simplest and most effective means of putting out traditional fires.