Water may not be safe to drink, cook or clean with after an emergency such as a flood. During and after flooding, water can become contaminated with microorganisms—such as bacteria, sewage, heating oil, agricultural or industrial waste, chemicals, and other substances that can cause serious illness.

If your area has been affected by flooding, your private water source may be contaminated. Flood water is likely to contain harmful microorganisms, dirt and chemicals. It is not safe to drink, cook or wash with water that has been affected by floods. For more information, read about private water supply management.

Floods are high volumes of water flow over areas that are normally dry land. Floodwaters can fully inundate water wells for days or weeks. The force of floodwaters can also disrupt or damage well or water supply infrastructure and directly introduce the contaminated water into the well.

Sometimes following a disaster, a boil water alert is issued for areas connected to mains scheme water because the mains water may be unsafe to drink or cook with. If a boil water alert has been issued, it is essential you follow this warning to prevent illness.

Use 2 drops of bleach per litre of water (or 1 teaspoon per bucket). Stir well and let the water stand for at least half an hour before use. Evaluate water that is to be used for hand washing, personal hygiene, floor washing, etc., based on appearance and smell.

Floods are often caused by heavy rainfall, rapid snowmelt or a storm surge from a tropical cyclone or tsunami in coastal areas. River floods are caused when consistent rain or snow melt forces a river to exceed capacity. Coastal floods are caused by storm surges associated with tropical cyclones and tsunami.

Causes of Floods

• Massive Rainfall. Drainage systems and the effective infrastructure design aid during heavy rains.
• Overflowing of the Rivers.
• Collapsed Dams.
• Snowmelt.
• Deforestation.
• Climate change.
• Emission of Greenhouse Gases.
• Other Factors.

What Causes Floods? Top 8 Common Causes of Flooding

• Heavy Rains. The simplest explanation for flooding is heavy rains.
• Overflowing Rivers.
• Broken Dams.
• Urban Drainage Basins.
• Storm Surges and Tsunamis.
• Channels with Steep Sides.
• A Lack of Vegetation.
• Melting Snow and Ice.

In the United States, there are five levels of flooding.

• Action Stage.
• Minor Flood Stage.
• Moderate Flood Stage.
• Major Flood Stage.
• Record Flood Stage.

In a small watershed, a storm can cause 100 times as much water to flow by each minute as during base-periods, but the river will rise and fall possibly in a matter of minutes and hours. Large rivers may take days to rise and fall, and flooding can last for a number of days.

Some of this water collects in large, underground reservoirs, but most of it forms rivers and streams that flow into the oceans, bringing the water back to its starting point.

Flood Factor works like this: Once you type in an address, the website produces a score on a 10-point scale (the greater the number, the greater the risk) to analyze the likelihood of a flood hitting your property. “Seeing your predictive likelihood of flooding is really, really useful,” Clark says.

How to read the flood data

Where Do Floods Occur? River floodplains and coastal areas are the most susceptible to flooding, however, it is possible for flooding to occur in areas with unusually long periods of heavy rainfall. Bangladesh is the most flood prone area in the world.

1. Flash floods. Flash flood is a flood which happens suddenly due to breach of water control structures, spillover or a heavy downpour in nearby areas. Normal floods occur gradually over many hours due to increase in water levels in rivers and water reservoirs, causing inundation.

Where, when, why and how — is complex. Here are five types of large-scale floods: flash, river, tropical/storm surge, tidal, and groundwater.

Floods come in all depths, from just a couple inches to many feet. The power of floodwater is extraordinary and lethal. In less than an hour, strong rain can turn an ankle deep creek into an unstoppable 30-foot-high swell that overpowers everything in its path. Floods occur all over the world.

The major cause of flood is heavy rainfall in the catchment areas of rivers and in the poorly drained areas. When the level of water rises above the river banks or dams, the water starts overflowing. The water overflows to the areas adjoining to the rivers, lakes or dams, causing floods or deluge.

Avoid driving through flooded areas and standing water. As little as six inches of water can cause you to lose control of your vehicle.

1. Avoid driving through flooded areas and standing water.
2. Do not drink flood water, or use it to wash dishes, brush teeth, or wash/prepare food.

Some of the common techniques used for flood control are the installation of rock beams, rock rip-raps, sand bags, maintenance of normal slopes with vegetation or application of soil cements on steeper slopes and construction or expansion of drainage. Other methods include dykes, dams, retention basins or detention.