Water covers around 70% of the earth’s surface, although not all of Earth’s water sits on its surface; much of it is stored in underground aquifers. The water in these aquifers is known as groundwater, and is what feeds our rivers and supplies much of our drinking water.
Although the most obvious water pollution is that which affects surface waters, as it is easy to see pollution on the ocean from an oil spill for instance, groundwater can also be polluted. Groundwater pollution tends to come from sources such as weed killers used in gardens that drain into the ground. Groundwater pollution may be less obvious than surface-water pollution, but it is no less of a problem.
Water pollution can occur in two different ways:
- Pollution can originate from a single source such as a factory’s discharge pipe, discharge from factory chimney, an oil spill from a tanker, or someone allowing oil from their car’s engine to flow down a drain – this is known as point-source pollution;
- Pollution can also occur from more than one source – this is called nonpoint-source pollution
In point-source pollution, the area where the pollution enters the environment is generally the most affected, therefore easier to contain if discovered soon enough. The longer it is left unattended the more chance the pollution has to disperse and pollute a wider area. Nonpoint source pollution is more difficult to contain as, by definition, it enters the environment from various places at once.
Point-source pollution can often affect areas up to thousands of kilometres away, such as can be seen by the way radioactive waste is carried by the oceans, for instance. A good example of this is the Fukushima Daiichi nuclear disaster that occurred at the Fukushima I Nuclear Power Plant in Japan in 2011 as a result of a tsunami.
The Fukushima disaster produced the largest discharge of radioactive material into the ocean in history, and traces of radionuclides were detected all over the world. Radiation also seeped into the groundwater, and it could take up to a hundred years to do a full clean-up.