Greywater may come from sinks, baths and showers, or from home hygiene and used utensils. Greywater means almost 50 % of the total amount of water used in hotels, residences, apartment complexes, sports facilities, etc. It can be distinguished from black water by the absence of bacteria Escherichia coli.

There is a demanding, accurate regulatory framework in Andalusian that controls grey and rainwater reuse: Regional Ministry of Leisure and Tourism’s Decree 47/2004. Article 49 defines greywater reuse and treatment’s requirements in hotel facilities.

Greywater reuse’s benefits include:

• A lower use of fresh water
• Less wastewater regeneration
• A high effective purification
• Only solution in certain places
• A lower energy and chemical use through pumping and treatment
• Plants can grow where there is any other type of water
• Recovery of lost nutrients
• An increase of knowledge and sensitivity about natural cycles

One of greywater main uses takes place in tanks, an element with an elevated level of consumption that requires a lower quality water. It cannot be directly used because it generates unpleasant odors and stains if it is left for more than a day.

They are a source of value as compost for agriculture. Although phosphorus, potassium and nitrogen make greywater a pollutant for lakes, rivers and groundwater, it can be advantageously used as nutrients for plants watering. Another possible use is outdoor areas cleaning.

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