The Effects of Floods on Sanitation

Our infrastructure is designed to deliver fresh water to our homes and offices and remove wastewater--either so-called "grey water" from uses like showers and dish cleaning or human waste and sewage. One of the great dangers of floods is not just the physical damage from floodwaters, but the health hazards of overwhelming municipal water systems. Floods can commingle clean water with water unsafe water.

Freshwater Systems

• There are many types of systems that deliver fresh water to people. Some are more vulnerable to contamination in a flood than others. Open water systems such as reservoirs can be very protected from floods, depending on their location. If they are elevated and buffered by vegetation, they are safer. If, however, they are at lower levels where high floodwaters might reach them, they could risk contamination. In a flood emergency, if you have any questions about the safety of your tap water, drink bottled water.

Storm Drains

• As with freshwater systems, there are many types of storm drainage systems from open culverts to large, cement-cast storm drains. These systems are designed by civil engineers to collect storm water and safely disperse it into waterways. There are many hazards with storm drains in floods. Chemicals that would not normally be waterborne, such as fuel or oil, can be swept in into the storm drains. Sewage from overwhelmed sewage systems such as septic tanks may also run into storm drains. Water that otherwise may not pose a great health hazard could become quite dangerous.

Urban Runoff

• Urban runoff is a concentration of chemicals built up on urban streets and sometimes commercial property such as filling stations. Under normal circumstances, urban runoff can be problematic in urban rivers and creeks. Creeks may be more polluted from "normal" runoff than industrial contamination. During and after floods, the runoff increases. And the soil can become supersaturated with water, which can flush dangerous chemicals out of the soil into waterways.

Sewage

• The same supersaturation that increases the dangers of urban runoff increases the danger of sewage contamination--in particular, the bacteria coliform. When water tables rise, municipal sewage systems as well as individual systems can dump untreated sewage into creeks and streams causing high levels of bacteria. Open waterways like rivers, bays and even ocean beaches, which are normally safe, may have an unsafe level of bacteria following a flood.