The waste water that runs off a car when it is being washed contains a range of substances that pollute the environment. These include detergents, degreasers, cleaning agents, oils, sediments (mud/grit and assicated contaminants like nutrients, heavy metals and bacteria) and other residue from car maintenance. When these substances enter the stormwater system they eventually end up in rivers, lakes, harbours and oceans.
Washing your car on a grassy area minimises runoff. The waste water is filtered by the grass and soil before it reaches the stormwater system and any pollutants are contained there. Nutrients from the waste water will be taken up by the grass and soil organisms will aid the breakdown of any biodegradable substances. This minimises pollutants reaching the stormwater system.
Most detergents contain sticking and wetting agents. Some are toxic to aquatic animal and plant life. This includes biodegradeable detergents. Some detergents contain chemicals such as phosphates, which act as nutrients and can, under the right conditions, lead to algal blooms, excessive plant growth and oxygen depletion of the water. This in turn leads to the death of aquatic fish and insects.
Commercial car washes treat waste water before disposing of it into the sewer system. Remember, a commercial car wash uses more water and soap than hand washing. Some newer car washes clean, recycle and reuse water. Check whether your car wash company recycles its water. The stormwater system is the drains, gutters, channels and pipes which collect rainwater and transport it, untreated, to streams, rivers, lakes, harbours and oceans.
Remember, the drain is just for rain.
The water that we wash the car with has undergone costly treatment to remove sediment and organisms that are harmful to our health. Another large cost in delivering it to your home is the electricity to pump it from the water collection area. These costs are covered by rates payments. An additional cost is the loss of natural biodiversity and natural landforms when dams and storage lakes are built.
During dry periods demand for water can be greater than the supply and this means we need to have costly storage lakes. Increasing demand on water supply due to lifestyle changes and an increasing population means that Greater Wellington Regional Council is now investigating future water supply and storage options.