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Reclaimed water

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Warning sign in Santa Monica, California, where reclaimed water is used to irrigate plants in public parks.

Reclaimed water is wastewater (sewage) that has been treated and purified to be as clean as (or sometimes cleaner than) standard drinking water. It is frequently used to irrigate golf courses and parks, fill decorative fountains, and fight fires. It can also be used to irrigate crops, as long as they will be peeled or boiled before human consumption.

Definition

Treated effluent from wastewater treatment facilities is typically discharged directly into a stream, river, or other location in order to recharge the water supply and promote natural decomposition of materials in the water that would not normally be able to be removed by standard treatment practices. Due to increasing population and demand for reliable fresh water sources, many areas around the world are now using reclaimed water to decrease potable water demands.

Reclaimed water is a most basic sense is treated effluent that would have normally been discharged into a natural body of water to contribute to the water recycling process. The difference is that reclaimed water is typically treated to a higher degree (depending on the location) and is used for a broad range of practical purposes, irrigation being one of the most common.

Many cities across the United States have exercised the use of reclaimed water as a result of discharge restrictions or low fresh water supplies. Water authorities in arid climates areas, supporting high populations, or having close proximity to oceanic saltwater intrusion have been the most proactive of all the users of reclaimed water.

Benefits

The costs involved with reclaimed water typically exceed those of standard potable water in most regions of the world, where a fresh water supply is plentiful. However, in areas where supplies of fresh water are limited, treating wastewater for reuse is becoming an economically attractive option, because it conserves drinking water. This is why many cities in Southwestern United States make use of reclaimed water.

Reclaimed water is usually sold to citizens at a cheaper rate than standard drinking water. It also contains higher levels of nitrogen and phosphorus, which help fertilize plants when used for irrigation.

Suitable for drinking?

Many cities are releasing reclaimed water in the "pottable" water pipes -whether directly or just by using river water that contains some water that has previously passed through a sewerage system. Reclaimed pottable water is free from viruses, bacteria, fungi, mould and other pathogens due to the use of chlorination and filtration. Very very small and hardy organisms such as cryptosporidium and giardia may survive chlorination. Cryptosporidium and giardia are present in all water supplies and its only a relatively high concentration that poses a risk. Only sub-micron filtration can remove all known organisms that are known to cause illness in humans.


Due to population increases and droughts (which are predicted to increase with global warming), many cities are now investigating potable use of reclaimed water.

'groundwater recharging or reservoir augmentation is where reclaimed water may be pumped into reservoirs where it will mix with (and be diluted by) rainwater. This mixture of rainwater and reclaimed water could then be treated again, and finally used as drinking water.

Many large cities using water from rivers are inevitably using water that came from treated sewage discharged upstream. It is sometimes said that water in London has been drunk five times before it arrived at the tap, but this is an exaggeration, as not much water in the sewerage is actually from human waste products (faeces or urine or other source ). There are many large towns on the River Thames upstream of London (Oxford, Reading, Swindon, Bracknell) that discharge their treated sewage into the river, which is used to supply London with water downstream. This phenomenon is also observed in the United States, where the Mississippi River serves as both the destination of sewage treatment plant effluent and the source of potable water.

Research conducted in the 1960s by the London Metropolitan Water Board demonstrated that the maximum extent of recycling water is about 11 times before the taste of water induces nausea in sensitive individuals. This is caused by the build up of inorganic ions such as Cl-, SO4--, K+ and Na+, which are not removed by conventional sewage treatment.


Reclaimed water that is not considered pottable is treated less than required for use as drinking water, and so non-pottable reclaimed water is not directly mixed with potable (drinking) water, for any use where it contacts humans. Those who irrigate their lawn or plants with reclaimed water should place a sign on their property warning people not to drink from the irrigation system.


The reasons that reclaimed water may need futher treatment to be pottable are

  • Extra filtering processes may remove minerals that are present in standard drinking water;
 (easily solved by dumping limestone rock into the system - this is actually a requirement to protect metal pipes from erosion.  )
  • humans may face psychological barriers against drinking reclaimed water (since it was formerly sewage);
  • small amounts of pharmaceutical chemicals may pass through the filtering process, potentially causing danger to humans. (eg hormones like oestrogen and progesterone)

Distribution and demand

Reclaimed water is distributed with a dual piping network that keeps reclaimed water pipes completely separate from potable water pipes. In the United States, reclaimed water is always distributed in lavender (light purple) pipes to distinguish it from potable water.

In many cities using reclaimed water, it is now in such demand that consumers are only allowed to use it on assigned days. Some cities that previously offered unlimited reclaimed water at a flat rate are now beginning to charge citizens by the amount they use.

A less elaborate alternative to reclaimed water is a greywater system. Greywater has been used in sinks, washing machines or showers, but does not contain sewage (blackwater). In a home system, untreated grey water may be used to flush toilets or for irrigation. In a city-wide system, grey water may flow in a set of pipes separate from other sewage to a treatment plant, where it can be treated and used in similar ways as reclaimed water.

Some locations using reclaimed water (for drinking water, unless marked otherwise )

See also

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