What is Gray Water?
The exact definition of gray water varies from state to state, but generally includes any household wastewater other than that which comes in direct contact with human waste (such as water used for toilet flushing) or that has the potential to contain a large amount of organic material (such as food waste from kitchen sinks). As defined in Chapter 381 of the Florida Statutes, gray water includes water from baths, showers, clothes washers, laundry trays, and sinks, but does not include wastewater from kitchen sinks.
Wastewater from toilets, urinals, and kitchen drains is classified as blackwater and must be directly connected to a public sewer or to an onsite sewage and treatment disposal (e.g. septic) system. Wastewater from kitchen drains is classified as blackwater due to higher organic contents (food waste) which can lead to greater microbial activity, and thus is of greater concern to public health. In some states laundry water may be considered as blackwater when used for washing materials soiled by human waste, such as diapers.
The average indoor water use in the U.S. is 69.3 gallons per person per day in 1999
Reusing gray water reduces the use of drinking-quality (potable) water for non-drinking quality (non-potable) needs. Potable water is often used unnecessarily around the household for purposes for which gray water would be acceptable. The average indoor water use in the U.S. is 69.3 gallons per person per day in 1999 and approximately 50–60% of this is used in showers, bathtubs, sinks, and as laundry water, while toilet flushing uses approximately 25%. Gray water is of lesser quality than tap water but is generally of higher quality than blackwater. Replacing some or all of the potable water used for non-potable needs (such as toilet flushing and irrigation of non-edible portions of the landscape) can significantly reduce demand for fresh water. Reducing demands on fresh water can reduce the need for new (and potentially costly) municipal sources of fresh water, reduce depletion of groundwater and associated environmental impacts, and reduce the volume of household wastewater sent to septic tanks or treatment plants.
Gray water must be filtered, disinfected, and dyed.
There are several requirements for gray water systems for flushing toilets (water closets) and urinals in Florida. Distribution piping must be clearly identified as containing non-potable water by pipe color or with metal tags. Gray water must be filtered, disinfected, and dyed. Gray water storage reservoirs must be appropriately sized and must have a make-up potable water supply. Storage reservoirs must also have drains and overflow pipes which must be indirectly connected to the sanitary drainage system. The main components of a gray water system for flushing toilets and urinals include filter system, storage reservoir, disinfection unit, and coloring dye injection unit. This document explains the gray water reuse systems in Florida:
For more information, contact:
Yilin Zhuang, Ph.D.