Graywater Reuse and Rainwater Harvestingby R. Waskom1
- Graywater reuse may not be a permissible use of water under a domestic well permit or a community water supply system.
- Rainwater harvesting is the process of intercepting storm-water runoff and putting it to beneficial use.
- The diversion and use of rainwater is subject to Colorado water law,
making it difficult to use without a plan for augmentation that replaces
depletions to surface water flows. In most areas of Colorado, the most common
way to use rainwater is to direct roof gutter downspouts to landscape areas
you wish to water.
Graywater refers to the reuse of water drained from baths, showers, washing
machines, and sinks (household wastewater excluding toilet wastes) for
irrigation and other water conservation applications. Contrary to common belief,
graywater is not a “safe” product—it contains bacteria and other potential
pathogens. Consequently, the potential reuse of graywater is a public health
issue, not a water conservation priority.
Graywater is of lesser quality than tap water, but generally of higher
quality than blackwater, or water from sewage systems. Water from the kitchen
sink, garbage disposal and dishwasher is considered blackwater in other states
because of high concentrations of organic waste and the difficulties of reusing
this water safely.
The most obvious advantage of domestic graywater use is that it may
potentially replace other water used for landscape irrigation. Filtered
graywater is most suitably used for subsurface irrigation of nonedible landscape
plants. Not only does its use on landscapes conserve treated tap water, but
graywater may also benefit plants because it often contains nutrients such as
nitrogen or phosphorus.
Graywater use may offer financial savings to already overburdened municipal
sewage treatment facilities because graywater use diminishes sewer flows,
thereby lessening the need to expand such facilities. However, diminished sewer
flows may have a downside because graywater use can result in insufficient sewer
flows to carry waste to the sewer plant. Another concern is that with increased
use of graywater, less effluent water will be available for treatment, resulting
in less reclaimed water for municipal uses and downstream appropriators.
Graywater systems vary from simple, low-cost systems to highly complex and costly systems. A common (but illegal in Colorado and most other states) method for reusing graywater is to drain the washing machine directly onto outside vegetation. Sophisticated systems treat graywater prior to disposal using settling tanks and sand filters in order to remove pollutants and pathogens.
Graywater is different from warm-up water (wasted tap water that is allowed to run down the drain before it reaches a desired temperature). Warm-up water that has not been used for bathing or dishwashing is generally free from bacteria and other pathogens. The amount of wasted warm-up water can be significant in homes where water heaters are located a considerable distance from showers or tubs and where no recirculation system is installed. Catching this water in a bucket and using it to water plants can contribute to home water conservation savings.
Water Quality Issues Surrounding Graywater Reuse in Colorado
Practically speaking, the use of graywater systems is not viable for most
homeowners in Colorado. Currently graywater is regulated under the State of
Colorado Guidelines on Individual Sewage Disposal Systems and applicable county
Individual Sewage Disposal System (ISDS) regulations. The Colorado Department of
Public Health and Environment (CDPHE) does not currently separate graywater from
blackwater in its regulations. Consequently, both surface and subsurface
applications require permitting and may trigger monitoring requirements.
If graywater is discharged in the soil below the root zone in the manner of a
leach field, a permit from the local Health Department is required. Your local
county Health or Planning Department will have specifications for adequate soil
cover for leach fields that amounts to a minimum of 18 to 24 inches of soil
cover. However, this deep application of the graywater will not meet the
practical needs of most homeowners, unless they want to install a windbreak of
trees or large shrubs. If graywater is used to irrigate below the soil surface,
but within the root zone (above frost line), a local permit plus monitoring is
If the graywater is applied to the surface, a means of disinfecting the graywater is necessary. Bacteria and other fecal borne pathogens in graywater are a concern and may require installation of advanced treatment systems. If estimations of graywater volume or soil intake rates are inaccurate, ponding or runoff can become a problem. Graywater may also contain sodium and chloride, which can be harmful to sensitive plant species. Research on the public health hazards of graywater use is limited, with no data indicating problems, or non-problems, for that matter.
Application of graywater from systems that discharge 2,000 gallons or more
per day requires a permit from the Colorado Department of Public Health and
Environment; smaller systems require permits from your local health
Municipal Applications: A graywater system is defined as a type of
individual sewage disposal system that requires the owner to secure an
installation permit from the local county Health Department prior to
construction. Many county ISDS regulations prohibit the issuance of any type of
individual sewage disposal system permit for a lot within 400 feet of service by
a municipal or community sewage treatment facility. Many municipalities have
similar connection and usage requirements that technically prohibit the use of
graywater in urban areas.
Rural Applications: On properties served by a permitted ISDS, a request to install a graywater system should be submitted to your local county Health Department. Many counties require the following criteria to permit a graywater system:
- The system must be designed by a registered professional engineer.
- The graywater plumbing system collection lines must be segregated from the blackwater (toilet) lines and must be a maximum of 2 inches in diameter.
- The graywater system design must meet all minimum design and construction standards of ISDS (except tank sizing).
- A graywater system must incorporate a first stage treatment unit consisting of a two-compartment septic tank (sized with a 30-hour detention time) or an NSF (National Sanitation Foundation) approved filtration or aeration tank unit.
- The graywater system design components must meet the minimum requirements for vertical and horizontal separation distances as defined in ISDS regulations. • For normal permitting processes, the final disposal of the graywater outflow must be to a subsurface absorption field meeting sizing, construction, and siting requirements.
- Graywater systems designed for use via sprinkler irrigation, direct surface application, or subsurface disposal to shallow soil depths must be sampled at least weekly for applicable effluent limitations as contained in the ISDS guidelines; the use of graywater for irrigation may also be subject to water rights limitations (as regulated through the Colorado Division of Water Resources) which should be confirmed prior to considering graywater reuse of any kind.
Water Rights Issues Surrounding Graywater Reuse in Colorado
If considering a graywater system where the source of water is from a well,
other issues must be considered. Well permits are issued pursuant to Colorado
statutes. The Colorado Division of Water Resources regulates well water permits
to prevent well pumping from injuring other water users. Graywater use may not
be a permissible use of water under a well permit and this must be clarified
prior to installing a graywater system. In some cases, the conditions of
approval under which a permit was issued would not prohibit the capture and use
of graywater. In other cases, the permit conditions would not allow it.
Specifically, if the permit was issued for ordinary household purposes inside a
single-family dwelling, with no outside uses, the capture and use of graywater
for any use outside the dwelling (including lawn and garden irrigation) would
not be allowed.
Well permits that were issued in areas of the state where the stream system
is not over-appropriated may qualify for use of a graywater system. Old wells
that are unregistered and were constructed prior to laws being enacted that
required a well permit, may qualify for graywater systems if the historical uses
included lawn and garden irrigation and they can be late registered pursuant to
section 37-92-602(5), CRS (2002). For wells operating under court-approved plans
for augmentation, the terms and conditions of the decrees entered would have to
be evaluated to see whether or not graywater systems would be allowed. In most
cases, these plans for augmentation rely in part on the return flows generated
by the individual well. In such cases, graywater systems might not be
Many of the permits issued throughout the state on parcels of land less than 35 acres contain restrictions that disallow the use of graywater. Permits issued on tracts of 35 acres or more with a return flow requirement could possibly utilize a graywater system if it is demonstrated that the actual depletion to the stream system was not increased.
Rainwater harvesting is the process of intercepting storm-water runoff and putting it to beneficial use. Rainwater is usually collected or harvested from rooftops, concrete patios, driveways and other impervious surfaces. Buildings and landscapes can be designed to maximize the amount of catchment area, thereby increasing rainwater harvesting possibilities. Intercepted water then can be collected, detained, retained and routed for use in evaporative coolers, toilet flushing, pet and car washing, indoor plant watering, pet and livestock watering, and for lawn and garden irrigation.
Rainwater harvesting systems vary from the simple and inexpensive to the complex and very costly. Typically, these systems are simple, consisting of gutters, downspouts, and storage containers. Directing rainfall to plants located at low points is the simplest rainwater harvesting system. In this system, the falling rain flows to areas with vegetation. Inexpensive rainwater storage systems commonly make use of above ground containers such as a barrel or plastic tank with a lid to reduce evaporation and bar access for mosquito breeding. Any container capable of holding rain dripping from roof or patio can be used as a rainwater harvesting system.
Water Quality Issues Concerning Rainwater Harvesting
Rain in urban and industrialized areas may contain various impurities
absorbed from the atmosphere, including arsenic and mercury. In Colorado, rain
is infrequent, but rainwater quality is generally very good. However, the
infrequency of rainfall results in accumulation of bird droppings, dust and
other impurities on rooftops between rain events. These impurities may occur in
high concentrations in rooftop runoff when it does rain. The best strategy is to
filter and screen out contaminants before they enter the storage container.
Dirty containers may become a health hazard or a breeding ground for mosquitoes
and other pests.
Various methods can be used to purify rainwater. First-flush devices ensure a
certain degree of water quality in harvested rainwater. The first several
gallons of runoff from a gutter, roof, or other surface are likely to contain
various impurities such as bird droppings and dust. A first-flush device
prevents this initial flow from draining into the storage tank. Many first-flush
devices have a simple design. Such devices include tipping buckets that dump
when water reaches a certain level. In addition, there are containers with a
ball that floats with the rising water to close off an opening after an inflow
of five gallons. Water is then diverted to a pipe leading to the storage
container. This use of simple technology is an attractive feature of rainwater
harvesting. Roof washing is not needed for water used solely for irrigation
purposes. However, pre-filtering to keep out debris will reduce sediment buildup
in the irrigation system.
Due to concerns surrounding microbial contamination of harvested rainwater, it is not recommended as a source of drinking water for humans. However, properly designed, constructed, and maintained systems that include disinfection steps have been successfully used for private domestic water supplies. Consult your local Health Department prior to constructing rainwater harvesting systems.
Water Rights Issues Concerning Rainwater Harvesting
The diversion and use of rainwater is subject to the Constitution of the State of Colorado, state statutes, and case law. New Colorado residents should understand that water rights in Colorado are unique compared to other parts of the country. The use of water in this state and other western states is governed by what is known as the prior appropriation doctrine. This system of water allocation controls who uses how much water, the types of uses allowed, and when those waters can be used. A simplified way to explain this system is often referred to as the priority system or "first in time, first in right."
An appropriation is made when an individual physically takes water from a stream or well (when legally available) and puts that water to beneficial use. The first person to appropriate water and apply that water to use has the first right to that water within a particular stream system. This person, after receiving a court decree verifying their priority status, then becomes the senior water right holder and that water right must be satisfied before any other water rights are filled. In Colorado, the State Engineer has the statutory obligation to protect all vested water rights. The process of allocating water to various water users is traditionally referred to as water rights administration, and is the responsibility of the Division of Water Resources.
Of course, the appropriation system is much more complicated than described
above. Some priorities on major stream systems in Colorado date back to the
1850's, and most of the stream systems have been over-appropriated, meaning that
at some or all times of the year, a call for water even by a senior appropriator
is not satisfied. Practically speaking, this means that in most river drainages,
a person cannot divert rainwater and put it to a beneficial use without a plan
for augmentation that replaces the stream depletions associated with that
diversion. In most areas of Colorado, the only sure legal way to use rainwater
is to direct roof gutter downspouts to drain to landscape areas you wish to
It is recommended that before you develop a rainwater harvesting system you check with the Colorado Division of Water Resources and your local building, zoning, and environmental departments to determine what plumbing requirements, local restrictions, neighborhood covenants, or other regulations or guidelines might apply to your project. Rainwater catchments, distribution systems, and landscape holding areas must be located and used entirely within the property boundaries of the individual or entity building using the system. These systems must be maintained in an acceptable manner and not cause damage or interference to neighboring property. Standards for construction must be consistent with industry standards or as determined by the local administrative authority.
For more information, contact your local county Health or Planning department or visit:
- Colorado Department of Public Health and Environment: http://www.cdphe.state.co.us/
- Colorado Division of Water Resources: http://water.state.co.us/
- CA Gray Water Central: www.oasisdesign.net/index.htm
- Graywater information: http://www.graywater.com/e_index.html
- American Rainwater Catchment Systems Association: http://www.arcsa.org/
- Texas Rain Water Collection information: www.twdb.state.tx.us/iwt/rainwater/docs.html
1 R. Waskom, Colorado State University Extension water resources specialist and director of the Colorado Water Resources Research Institute. 4/03. Revised 3/08.
Colorado State University, U.S. Department of Agriculture and Colorado counties cooperating. CSU Extension programs are available to all without discrimination. No endorsement of products mentioned is intended nor is criticism implied of products not mentioned.
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