Inadequate provisioning of water or the rapid deterioration of the quality of the same presently represents a serious problem for many towns, industries and also for farming.
Various factors have contributed in creating this situation, starting from the increase in population in certain urban areas, the contamination of the groundwater tables and problems of distribution of water itself.
The re-use of water has been defined as the biggest challenge of the 21st century, considering the fact that the worldwide population is increasing while water resources remain the same or even drop drastically in certain areas.
The re-use of water has two important functions:

• The effluent conditioned is used as a resource to create benefits.
• The effluent conditioned is kept away from surface water such as lakes, rivers and seas, thus further limiting possible causes for pollution.

The main factors around which the re-use of water revolves are the following:

• A safe conditioning system of drained water to comply with the purposes requested.
• The safeguarding of public health.

Water recycling systems must be carefully planned and designed in relation to the area in which they are installed in order to have the degree of flexibility suitable for the demands, even immediate, of water.
There are mainly three classes of substances that need to be considered when drained water is conditioned for re-use:

• Viruses and pathogenic germs in general.
• Organic constituents including chemical products, detergents and so on.
• Heavy metals.

The impact of many of these traces or large quantities of constituents on human health on the long term is not often fully comprehended and therefore the technique required to be able to re-use water effectively is often underestimated.
The “closure” of the water cycle for towns or industries is not only a hope but is also an economic justification.
To conclude, the re-use of water has become an essential element to be able to hoard the available water resources.