Greywater, usually defined as “untreated waste water which has not come into contact with toilet waste”, is used as a supplementary irrigation supply for watering plants. Because most greywater systems do no include large cisterns or storage tanks the greywater must be used promptly or it is piped off to the sewer.
In areas with a year round irrigation season, greywater can be used continuously. However, much of the country where the growing season ends in the fall cannot make use of greywater for a substantial part of the year. Theoretically greywater could be used to water indoor plants during the winter months, but this could prove problematic if the greywater system does not provide sufficient filtration to remove potential sources of odor and bacteria.
Because of these seasonality issues, greywater systems are more practical and cost effective in warmer climates with longer irrigation seasons.