Air and Water Pollution
Prevention and Control Engineering
Residential Rainwater Harvesting
And Grey Water Recycling
Bill Bardin
RPI – Fall 2013
Professor Gutierrez-Miravete
Residential Rainwater Harvesting and Grey Water Recycling
RPI – Fall 2013
Professor Gutierrez-Miravete
Bill Bardin
Table of Contents
RESIDENTIAL RAINWATER HARVESTING AND GREYWATER RECYCLING
1
INTRODUCTION
2
RAINWATER HARVESTING
2
GREY WATER RECYCLING
7
CONCLUSION
9
REFERENCES
10
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Residential Rainwater Harvesting and Grey Water Recycling
RPI – Fall 2013
Professor Gutierrez-Miravete
Bill Bardin
Rainwater Harvesting
Introduction
In recent years, rainwater harvesting has emerged as a water conservation tool and an
alternative water supply source, especially in arid areas of the United States. Escalating
costs of centralized water systems and well drilling, an increasing recognition of the
beneficial qualities of rainwater and dwindling water supplies are contributing to this
trend. Interest in rainwater harvesting has also been spurred by the prospect of rising
municipal water demand resulting from the enormous population growth.
Rainwater harvesting is nothing new. Humans have been harvesting rainwater since we
first began to walk erect on this planet. Harvesting rainwater is only a small part of the
entire water cycle, but it is of growing importance. It’s not just about harvesting the
rainwater but efficient use of all our water resources.
Many communities in the United States face serious threats to a safe, steady supply of
water. These include a longstanding reliance on centralized water delivery systems that
results in urban areas and agencies largely overlooking opportunities to integrate alternate
local sources of water to meet their water supply needs. One of the biggest offenders is
the unnecessary use of potable water for non-potable uses, such as irrigation and indoor
toilet flushing. The continually increasing areas of impervious surfaces, parking lots
driveways, sidewalks and buildings in our landscape result in storm water runoff carrying
pollution to our rivers, lakes, and beaches. Although the problems of water supply and
water pollution can be complex, practical solutions for both are available now, such as
capturing and using rainwater from rooftops.
Rooftop rainwater capture is a simple, cost-effective approach for supplying water that
promotes sustainable water management. By using rainwater rather than allowing it to
run off of paved surfaces to pick up pollutants and carry them to nearby surface waters.
Simple rainwater capture can provide numerous benefits to the local environment.
Rainwater capture is an inexpensive, on-site supply of water that can be used for outdoor
and non-potable uses with little, if any, treatment. In many cases captured rainwater can,
and is used as a potable water supply with appropriately higher levels of treatment such
as multi stage filtration and ultraviolet sterilization. One of the big advantages of using
captured rainwater is minimal, or no energy and economic costs associated with treating
and delivering potable water to end users because capture systems can often be designed
using low-volume, non-pressurized, gravity fed systems or require only the use of a low
power pump for supply, especially in the more arid areas of the United States where
prolonged sub-freezing temperatures are present. By capturing and using rainwater for
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Residential Rainwater Harvesting and Grey Water Recycling
RPI – Fall 2013
Professor Gutierrez-Miravete
Bill Bardin
irrigation and other non-potable uses we are reducing the load on the potable water
system, reducing the electricity to treat and pump that water and reducing the use of
chemicals used in the purification. It also eliminates the addition of chemicals, chlorine
and fluoride directly into the ecosystem.
Reduced runoff that would otherwise contribute to storm water flows which is a leading
cause of surface water pollution and urban flooding could be significantly reduced with
rainwater capture. High periods of rain, during which most of the water runs off into the
streams and rivers, can be captured and distributed over longer periods of time,
maximizing the effectiveness of the water source.
In the arid southwestern area of the United States the population is expected to double
over the next fifty years and demand for water supplied from municipal sources is
projected to double over the same time period. This problem is compounded by the fact
that existing freshwater supplies are, for a variety of reasons, expected to decrease during
that same time period. Increased loads on the water system from the agricultural demands
of an exploding population place additional pressure on the total water supply making
new farming methods and conservation essential. A repeat of the “Dust Bowl” era, 1930
– 1939, could prove catastrophic to the food supply in the United States. During the dust
bowl era, over 10 million acres of land in the southwest and high plateau of the eastern
Rocky Mountain area were stripped of their serviceable topsoil, an estimated 4.8 billion
tons.
The main source of water for the area, the Ogallala Aquifer, is being depleted at an
alarming rate. A study by Kansas State University in Manhattan, Kansas, was recently
published on in the journal Proceedings of the National Academy of Sciences. According
to the study, the Ogallala Aquifer will see a 39 percent depletion of its available
groundwater over the next five decades, which is in addition to the 30 percent reduction
that the water supply has already recently faced. In response to this alarming condition,
the State of Colorado, in 2009 passed laws outlawing the capture of rainwater. They have
since relaxed some of these restrictions but the basic law remains in place. Other states,
like Texas have actively promoted rain harvesting especially in the western areas of the
state where rainfall totals less than 10 inches a year.
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Residential Rainwater Harvesting and Grey Water Recycling
RPI – Fall 2013
Professor Gutierrez-Miravete
Bill Bardin
Quite simply, rainwater harvesting is the capture and storage
of rainwater for use. A rainwater harvesting system can be as
simple as channeling the rain that runs off of a roof into a
barrel or cistern or as sophisticated as a system made up of
pumps, filters and water treatment equipment.
Regardless of its complexity, a rainwater harvesting system
consists of six parts: a catchment surface such as a roof; a
channeling system such as gutters and downspouts; a screen
or diverter; storage tanks such as barrels or cisterns; a
delivery system such as pumps; and if the end use requires it,
a treatment system such as sediment filters and ultraviolet
lamps.
Simple Rainwater Collection (2)
Simple systems can supply water
for lawns and other non-potable
uses while more sophisticated
systems, if properly designed,
constructed and operated, can
provide potable water.
Costs for a rainwater harvesting
system can range from a few
thousand dollars to tens of
thousands of dollars depending on
size and complexity.
Complex Rainwater Collection System (3)
The volume of water that can be
collected by a rainwater harvesting system depends primarily on two factors: the
catchment area and the amount of rainfall. For every square foot of catchment area, about
0.62 gal of water can be collected for one inch of rainfall. For example, if a house with a
roof area of 2,000 ft2 receives 1 inch of rainfall, the volume of water that the homeowner
can expect to realistically collect is about 1,240 gal.
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Residential Rainwater Harvesting and Grey Water Recycling
RPI – Fall 2013
Professor Gutierrez-Miravete
Bill Bardin
Is harvesting rainwater a good
investment? Like most things it
depends on your social view
and commitment to improving
the environment. For those
taking the “Do no harm”
approach, rainwater recycling
can be a good, economical
starting point.
Rainwater harvesting systems
can deliver a good return on
investment. In certain areas of
the country and the world,
catching
rainwater
for
Typical Rainwater Harvesting System (4)
household use is the only costeffective solution. In locations
like the US southwest, and arid rocky areas where no municipal water system is available
and where well drilling can be prohibitively expensive, harvesting rainwater is a smart
economic and environmental choice. On many Caribbean Islands, rainwater harvesting is
the only reliable source of residential water, due mostly to the lack of infrastructure and
relatively low population density. With the ever-rising costs of utility water, rainwaterharvesting systems can now make good financial sense for homeowners in high-waterrate areas typically in the western half of the United States.
It’s not just the direct demands of population growth that are impaction our water
resources. In 1973 the United States experienced the first of several oil crises. In an effort
to wean ourselves from oil, the US mandated the use of ethanol as a fuel additive. In this
country, ethanol is primarily produced from corn. The process uses exorbitant amounts of
water. Petroleum refining consumes 1-2.5 gallons of water per gallon of refined product.
Colorado scientists Kreider and Curtiss estimate that refining a gallon of corn ethanol
today requires thirty-five gallons of water. But that is only the beginning. Kreider and
Curtiss estimate that three times as much water is needed to grow the corn that yields a
gallon of ethanol. That brings the tally to 140 gallons of water per gallon of corn ethanol
produced. (6) If their calculation is correct, the 5.4 million gallons of corn ethanol used in
America in 2006 required the use of 760 million gallons of fresh water. (7)
Because of demands like ethanol production, water rates can be expected to continue to
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Residential Rainwater Harvesting and Grey Water Recycling
RPI – Fall 2013
Professor Gutierrez-Miravete
Bill Bardin
increase faster than the rate of inflation, so in more areas rainwater harvesting will make
great economic sense. These increases are being driven by population growth and
demand, diminishing fresh water supplies, and greater costs to process water to make it
drinkable. Increased costs will spur more conservation, but it will also make the option of
rainwater harvesting more viable for people. Many cities have such an old water delivery
system that routine maintenance costs are rising at a rapid rate. New York City is
spending billions of dollars to dig a new water aqueduct to bring water from the
Adirondack Mountains north of the city. This is to supplement the existing lines that are
over 100 years old.
So is it worth it? Because of the number of variables, current water costs, expected
increases, rainfall rates, household use rate, etc. It is very hard to determine the financial
viability of a system. Each system needs to be evaluated on it’s own merits.
The typical payback period for projects in the business world is three years. Projects that
take longer to pay back typically require long-term financial justifications. Unless
rainwater harvesting is essential to survival of the homeowner or the homeowner is
socially committed to the environment, these systems do not come with a strong financial
payback. Although the return on a rainwater system will only improve over time as utility
water rates rise.
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Residential Rainwater Harvesting and Grey Water Recycling
RPI – Fall 2013
Professor Gutierrez-Miravete
Bill Bardin
Grey Water Recycling
There are four basic types of water used in residential structures:
 White water – Potable water
 Grey water – Shower, Bath, Laundry, Lavatory Basin
 Dark water – Kitchen waste, food, strong detergents
 Black water – Toilets, Laundry (if washing diapers, etc.)
For the purposes here I am dealing only with recycling grey water. Grey water can be
defined as any household wastewater with the exception of wastewater from toilets,
which is known as black water, or kitchen waste which may contain foodstuffs.
Typically, 50-80% of household wastewater is grey water from bathroom sinks, tubs and
showers. Freshly generated grey water is not as offensive as black water, but if it's not
handled properly it can soon become so. Grey water decomposes at a much faster rate
than black water and if stored for as little as 24 hours, the bacteria in it use up all the
oxygen and the grey water becomes anaerobic and turns septic. At that point it is more
like black water, a health hazard. Many jurisdictions have strict regulations about
disposal of grey water, and some even prohibit it’s reuse or direct disposal. The safest
way to handle grey water is to introduce it directly to the topsoil layer, where soil bacteria
can quickly break it down, releasing the nutrients available to plants.
Almost half of the water consumed by the average household in North America is for
outdoor use, which begs the question, “Why use treated, potable water, if you don’t need
to?” Capturing the grey water for use outdoors can cut water usage in half. There are
additional benefits to be gained by using grey water. By diverting the grey water from
the septic system extends the life and capacity of the system. If you are on a municipal
sewer system, diverting grey water reduces the load. Grey water recycling for irrigation
replenishes groundwater, helping the natural water cycle to keep functioning. Grey
water can support plant growth in areas that might otherwise not have enough water, like
the arid southwest. The nutrients in the grey water are broken down by bacteria in the
soil and made available to plants. This helps to maintain soil fertility. The grey water
user gets the satisfaction of direct participation in the responsible management of global
nutrient and water cycles.
In addition to applying grey water directly to the soil, it is possible to recycle it into the
home for use in toilets to further reduce the water load of the home. This requires a
significant investment in equipment and creates an ongoing maintenance commitment to
be effective.
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Residential Rainwater Harvesting and Grey Water Recycling
RPI – Fall 2013
Professor Gutierrez-Miravete
Bill Bardin
As with any system of this type, the local environment must play the major roll as to
the overall viability. For grey water recycling the type of soil plays a large part. If your
soil is either too permeable or not permeable enough, you may not be able to recycle
your grey water, or you may need a system with some modifications. The amount of
grey water produced is also an important factor in the effectiveness of the overall
system. It is essential that you have enough soil available to process the grey water and
enough plants to use it.
Since grey water recycling is a relatively new technology, many cities and towns have
no clear guidelines regarding grey water processing. With water shortages looming in
the near future for many regions, this may change sooner than later. Health concerns are
often cited as the reason for not allowing grey water recycling, although the possibility
of becoming sick is minimal with a properly designed, installed and maintained grey
water system.
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Residential Rainwater Harvesting and Grey Water Recycling
RPI – Fall 2013
Professor Gutierrez-Miravete
Bill Bardin
Conclusion
Both rainwater harvesting and grey water recycling are viable solutions to the growing
water crisis. The ever changing climate on the planet which is exacerbated by, for lack
of a better term, global warming, continues to put pressure on the global ecosystem.
With the population expected to reach 7 billion in the next 6 years and 11 billion by
2050, there will be significant burdens placed on all our natural resources, especially
water. (8) For example, Iceland, that gets 75 percent of it’s electricity from hydroelectric
sources, primarily glacial runoff, projects that they will run out of water in 100 years.
Even though the surface of the planet is 70 percent water, only 1 percent is potable.
There are solutions to the water issue, iceberg harvesting, desalination, etc. but these
tend to be very energy intensive and, at present, cost prohibitive.
Rainwater harvesting makes sense in most areas of the world and grey water recycling
can supplement our water use but both require a social and economic commitment. The
biggest commitment being the social one. Only people on the ‘fringe’ are early adopters
of programs that recycle, reduce, reuse, and even up cycle the products and resources we
use today.
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Residential Rainwater Harvesting and Grey Water Recycling
RPI – Fall 2013
Professor Gutierrez-Miravete
Bill Bardin
Reference
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
http://harvesth2o.com
http://www.edwardsaquifer.net/rainharvesting.html
http://vwrrc.vt.edu/swc/NonPBMPSpecsMarch11/VASWMBMPSpec6RAINWATERHARVESTING.html
http://www.britanniarainwater.co.uk/harvesting.html
http://www.newsmax.com/TheWire/ogallala-aquifer-water-supply depletion/2013/08/29/id/522910#ixzz2mcmal6IV
19. Jan F. Kreider and Peter S. Curtiss, "Comprehensive Evaluation of Impacts from Potential, Future Automotive Fuel
Replacements."
20. Calculation by author. Annual ethanol consumption estimate for 2006 is from the Renewable Fuels Association,
available at www.ethanolrfa.org/industry/statistics/#D (accessed July 23, 2008).
http://www.un.org/esa/population/publications/longrange2/WorldPop2300final.pdf
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