Higher water rates, surcharges for excess water use, and extensive local and regional droughts stressing water supplies are all driving the worldwide push to tap alternative sources of water for potable as well as non-potable uses. The increasing adoption of rainwater capture and reuse strategies is largely driven by economics. Those accustomed to opening the faucet, irrigating landscaping, flushing toilets, and regular high water use activities without worry are now experiencing a crunch of higher rates for a dwindling natural water resource.
Engineers who in the past could count on low water rates and an ample supply of potable water for developments are finding in some cases that no water can be found. And, it’s not just in the arid West. Diminishing groundwater supplies due to a lack of groundwater recharge is a national and international problem.
The extensive centralized wastewater treatment boom of the past — where water is taken from the aquifer, consumed, and disposed of through discharge far away from the source — is leaving local aquifer supplies diminished. Add to that the impact of siphoning natural water supplies upstream or even in other states to provide for the water needs of population centers, and then discharging it far from the point of origin. These activities, coupled with lean rainfall amounts and in some cases drought conditions (see Figure 1), are extracting a water resource toll even in unexpected areas.
Rainwater harvesting and reuse is one answer that can enable development where water resources are limited. It sounds great, but in some areas local building codes do not include rainwater capture for potable use, even though the technology and proven designs of these systems are well documented.
To assist engineers, designers, plumbers, builders/developers, local government officials, and end users in safely implementing a rainwater catchment system using precipitation from rooftops and other hard, impervious surfaces, the American Society of Plumbing Engineers (ASPE) and the American Rainwater Catchment Systems Association (ARCSA) with co-sponsorship by the International Association of Plumbing and Mechanical Officials (IAPMO) and NSF International, did gain approval for rainwater catchment systems as an American National Standard by ANSI in 2013. The ANSI standard states that collected rainwater can be subsequently used for irrigation, laundry, hygiene, or even potable water applications if the appropriate treatment and materials have been certified for the specific end use. Existing NSF/ANSI standards covering roofing and collection system materials and treatment devices for potable water applications are referenced in the standard.
Large community and commercial systems
Non-potable uses of rainwater and stormwater BMPs have been incorporated in forward facing communities and large cities nationwide for some time. Examples include Reno, Nev., and Chicago.
Truckee Meadows, Nev. — Just outside of Reno, Nev., a region called Truckee Meadows has many commuting residents. The climate is arid, with low humidity and an average annual rainfall of approximately seven inches. The Truckee River bisects Truckee Meadows into north and south sections and provides the major source of drinking water supply to the area, as well as recreational opportunities and habitat for fish and wildlife. Most of the stormwater that drains into the Truckee Meadows municipal storm drain system is conveyed untreated to the receiving waters of the Truckee River, and to three playas in unincorporated Washoe County.
Total Maximum Daily Load (TMDL) requirements have been established for the Truckee River, addressing three pollutants: nitrogen, phosphorus, and total dissolved solids. Nitrogen and phosphorus concentrations in the river have historically caused excessive plant and algal growth, which depletes oxygen when the plants die and decay. The community had all of the stakeholders involved to develop a BMP manual. With the program’s implementation, structural BMP’s were constructed, including rain gardens, vegetated swales, and other natural features, that would return the water to the aquifer.
Chicago — Stormwater management in Chicago is part of a larger citywide initiative to become “the greenest city in America.” The city’s first stormwater conveyance system was built in 1856. Similar to most cities of this era, it was constructed as a combined sewer system. Managing one of the largest wastewater collection and treatment systems in the world at a tremendous cost, the city still experiences urban runoff challenges.
Like most cities with combined storm and sanitary sewer systems, Chicago has invested in a hard pipe solution to expand capacity and reduce combined sewer overflows during significant flood events, but in Chicago, this is not viewed as the only solution. The city is a proponent of sustainable green infrastructure approaches to stormwater management, including landscape-based runoff reduction and onsite detention, water quality treatment, and infiltration.
Small communities and residential development
Due to advances in treatment technology, small communities and individuals are getting into the rainwater harvesting act as the need for alternative water sources for potable and non-potable uses escalates. In the case of one North Carolina homebuilder, what started as a good idea as part of the design of a LEED Platinum home turned into a necessity when well drilling to 605 feet failed to yield water.
The challenge — One would tend to think that in the humid, wet, East Coast climate, water is readily available everywhere; however, a homeowner outside of Raleigh, N.C., was in for a surprise. The project — a 4,800-square-foot home with a closely coupled 3,200-square-foot shop designed to achieve LEED Platinum Certification — is under construction in an area that is not served by public water. The drill location was just over a half mile away from Falls Lake, Raleigh’s water supply reservoir, and it was only about 150 feet away from an old dug well that is on an adjacent property. Thus confident that a drilled well could provide ample water to supply all of the resident’s needs, the homeowner began drilling, only to find that even at a depth of 605 feet no water was found.
The solution — Mike Stroud and Rain Pro of High Point, N.C., investigated the feasibility of installing a stand-alone whole-house potable water system with water supplied from the roof surfaces. With a total roof surface area of 11,000 square feet available from the home and garage structures, a 1-inch rain event would yield 6,860 gallons — ample water supply for the homeowner’s needs. Based on the average daily water consumption at the homeowner’s previous house, this is enough to supply three months’ worth of water.
Rainfall averages 40 to 45 inches per year in the region, which is a sufficient supply to meet the needs of the home. The roofs for both structures are single-slope, standing seam metal roofs, making them ideal for collecting rainwater by minimizing contaminants picked up from the roof. The system designed by Stroud collects rainwater from the roofs via leaders and piping and directs it to a series of storage tanks.
The water is piped from the buildings in Schedule 40 PVC piping and then through a filter (rated for a roof area as large as 16,000 square feet) that will allow nothing larger than 350 microns to enter the tanks. Because the first flush typically includes higher levels of contaminants, the first 120 gallons of water is diverted away from the tanks into a pipe, which discharges to a separate location (see Figure 2). Once the pipe is filled, a valve closes and the remaining flow from the rain event enters the storage tanks.
Four, Infiltrator IM-1760C, 1,787-gallon potable water tanks are installed in series and connected at the bottom to function as one large tank and to yield a total storage volume of more than 7,000 gallons. The Infiltrator tanks are NSF/ANSI Standard 61-certified for potable water storage, meeting a rigorous set of national standards to ensure potable water storage safety.
The tanks are buried outside the home and a submersible pump in the last tank in the series supplies water into the home. Prior to consumption, the water is pumped out of the tank and is treated via a set of three filters in an assembly: The first is a 20-micron filter, then a 5-micron filter, and finally with a 1-micron carbon filter. Following the filtration process, the water is disinfected via ultraviolet light. At this point, the water quality exceeds all applicable Wake County and North Carolina potable water standards and is ready for home use.
The system design will enable the homeowner to do most of the system management. The prefilter has a self-cleaning feature that minimizes required maintenance; required maintenance is fairly simple because the filter assembly is easily removed. The cartridge filters enable easy filter changes — there are shut-off valves on both sides of the filter assembly. The UV filter is also designed for easy maintenance; the bulb can be changed without having to disconnect any water lines. The UV bulb will be changed annually and the other filters will need cleaning or replacement every four to eight months, depending on conditions.
Large or small, individual or community systems, rainwater harvesting system designs are being adapted to suit a variety of potable and non-potable needs. What they all have in common is that they provide the life-giving resource of water and enable environmentally sound development where it would previously have not been possible.
Dennis F. Hallahan, P.E., technical director, Infiltrator Water Technologies (infiltratorwater.com), has more than 25 years of experience with onsite wastewater treatment system design and construction. He is responsible for technology transfer between Infiltrator Water Technologies and the regulatory and design communities and consults on product research and testing for universities and private consultants. He can be contacted at firstname.lastname@example.org.