Uses of Rainwater and Gray Water



You can collect a lot of rainwater with an ECOVIE system!

Roof(Square Feet) Atlanta Collection Potential (gallons)*
Gallons per Inch 2007 Totals 2013 Totals 30 Year Average
2,000 1,200 36,000 79,200 56,000
3,000 1,900 54,000 125,400 84,000
4,000 2,500 71,000 165,000 112,000
5,000 3,100 89,000 204,600 141,000
6,000 3,600 107,000 237,600 169,000
20,000 12,000 384,000 792,000 600,000

* assumes 10% loss due to evaporation and other factors

Outdoor Rainwater Usage:


Water usage varies from person to person and property to property. According to the EPA’s reported usage data, the average US household of four uses over half of their total water consumption outdoors in applications such as watering, irrigation, pool filling, and car washing. These types of water usage are the prime targets for rainwater collection systems.

For commercial scale projects a major application of captured rainwater is for cooling tower make up, typically one of the highest water demands for large facilities.

Indoor Rainwater Usage:

Indoor use of rainwater for laundry and toilet flushing (not to be confused with gray water recycling or re-use) is the next potential application after outdoor applications. If your outdoor water usage rate is low and you are doing a major remodeling or building a new home or commercial building the added cost of piping for bringing rainwater indoors is low. If this is your situation, you may be a strong candidate for this application.

For commercial properties, collected rainwater can be used for cooling tower make up and many process water applications.

Some jurisdictions require fine filtration and disinfection treatment for indoor non-potable uses which ECOVIE can design and specify for you. We can give you references of completed projects of installations where rainwater is used indoors.

Indoor drinkable (potable) applications also represent 20-40% of total household use. Using rainwater for indoor drinkable applications is definitely feasible and is a practice in many regions of the US and the world. ECOVIE has designed and installed potable rainwater systems and developed technical code and guidelines for its use in Atlanta.

Regardless of the application, rainwater harvesting makes sense on many fronts. Check out the next sections to find out why.

Gray Water:

Gray water is water that is sourced from inside a building and is available for reuse or recycling. Prime examples of gray water sources are from showering/bathing and from laundry.  Scale can be both residential (single family homes) and commercial (dorms, hotels, apartments).  The term gray water is often confused with rainwater used indoors.  Rainwater is never gray water and vice-versa.  Rainwater is not re-used water any more than our typical tap water is re-used. Of course, thinking about the hydrological cycle, we know that ALL water is “re-used” in some sense. Gray water is truly re-used or recycled on site.

Raw gray water typically has heavy biological load while raw rainwater does not. Therefore treatment requirements are quite different to achieve any given end use water quality requirement.

Gray water systems treat water to the level required for its end use as recycled or re-used water.  Many gray water system simply coarse filter water for same day irrigation use using subsurface irrigation.  Heavy biological load means that storing raw gray water will quickly morph into septic black water with no biological treatment.

Other types of gray water treatment include adding biological treatment such as that used with the Intewa AQUALOOP process.  With biological treatment, water is suitable for more applications like for laundry and toilet flushing and is also able to be stored.  This gray water treated with the AQUALOOP process is suitable for broadcast irrigation.

Another prime source of very clean gray water that can be used with little or no treatment for outdoor irrigation and cooling tower make up is HVAC condensate. In homes, it is easy to direct condensate to the rainwater storage system. For commercial operations, condensate generation can be high enough to yield thousands of gallons per day, which gives a steady and reliable source of water in the summer time.