There are classes of water damage that differ in the magnitude of the flooding. These classifications are determined with the magnitude of the damage done to the house. And then theres category of water damage which is determined through the waters level of contamination. The aforementioned worst case scenario is when the magnitude of damage is the worst and so is the water contamination.
The first category of water damage is if it is done by clean water. This water is one that comes directly from a clean source such as the faucet. Its relatively rare for water damage to be inflicted by clean water because it can easily become contaminated and categorized to the next.