Why a Flood Is Dangerous

A flood situation puts you at risk for electrocution if you make physical contact with floodwaters and your home is not fully disconnected from the grid. Never go into a flooded basement until a licensed electrician or emergency worker (such as from the fire department or utility company) has fully disconnected your home from the grid. Even if you’ve lost power during a storm, a neighbor running a generator could be enough to back feed electricity into your home and put you at risk for electrocution. Flash floods are dangerous. In general, there are three types of floodwater you might encounter. Clean water and greywater floods are usually confined to the home, while blackwater floods can happen at home but also on a larger scale.


Blackwater refers to wastewater contaminated with human waste. The citywide floodwaters we see on television are blackwater. Raw sewage is classified as blackwater. Blackwater is a haven for dangerous bacteria and pathogens that must fully decompose before being released into the environment. It can also be contaminated with dissolved chemicals and particulates, making contact even more dangerous.

When it comes to flooding emergencies, blackwater floods are the most dangerous and the most destructive. Because of the grossly unsanitary conditions of the water, porous and absorbent items such as carpets, upholstery, and drywall are often unsalvageable. Contact with blackwater via ingestion or skin contact can cause illness in both humans and pets.

Clean Water

Floodwater that does not pose an immediate health threat is known as clean water. Clean water floods can result from malfunctioning appliances, toilet holding tanks, and melting snow and rainwater. Clean water home floods are generally safe for you to clean up yourself, but standing clean water can become greywater in as little as 48 hours.


Greywater, or sullage, refers to wastewater that is not contaminated with fecal matter. It generally contains fewer pathogens than blackwater and can be reused for non-potable purposes, such as toilet flushing. Greywater still contains small amounts of contaminants and can induce illness if ingested. Greywater cleanup must begin immediately--greywater can become blackwater in as little as 48 hours.