When your property is provided water via rain, why let that "free" water literally go down the drain?
The practice of rainwater harvesting is becoming more prevalent as water costs rise. Companies are turning to rainwater harvesting systems in order to supplement the water needs of their facilities.
"It's an age-old practice that has gained popularity as fresh water resources become more scarce – whether due to drought, water pollution, or crumbling water infrastructure," says Mike Ruck, vice president of the American Rainwater Catchment Systems Association (ARCSA) and chief water officer for RainWater Solutions in Raleigh, NC.
Rainwater can fulfill a multitude of uses when harvested. "Rainwater is naturally soft and, in most areas, pH neutral to slightly acidic," Ruck explains. "The water can be used for any and all water needs – from consumption to irrigation. The end use will determine the complexity of the system and how much filtration is required. For irrigation and other non-potable uses, filtration is generally very basic. For water to be consumed, it will need to be cleaned and filtered to a higher standard."
Both the ability to harvest and the uses for reclaimed rainwater vary from state to state and even city to city, mostly due to differing opinions on ownership of the water. "Water rights and restrictions are on a state-by-state basis," he says. "You certainly do have to check locally how the water rights are set up in your state. In Colorado, where just recently it became allowed to collect rainwater on a limited basis, it's going to be very different than it is in North Carolina, where you're free to collect and use the rainwater as it hits your property."
From Retention to Reuse
Built in 1913 and previously owned by A.R.C. Inc., the historic Hurt Building in downtown Atlanta was bought by Harbor Group International in 2006 before it achieved LEED-EBOM Gold Certification in 2009. Even though the price of water in Georgia continues to rise, saving money on water purchasing wasn't the primary goal for A.R.C. Inc. when it installed a rainwater retention system.
"The previous owners installed the system to keep the basement from flooding," says Virgil Sudduth, chief engineer for the Hurt Building. "The basement of the building sits on top of groundwater. There's a trench system that runs through the basement so that the water coming from the ground to the surface can run off. The problem is that the roof drains were all brought down through the building and tied into this trench drain system. When it rained, the system was overwhelmed and the basement flooded."
To remedy the flooding, A.R.C. Inc. installed two 500-gallon tanks. The roof drain system is attached to the tanks so that when water falls onto the building's roof, it drains directly into the tanks. When the tanks fill up to a prescribed level – around 80% full – the water is pumped out of the building and into the city storm sewer system. "When it's raining outside, the tanks are constantly filling and being pumped out, in an effort to keep that water from overwhelming the underground trench system," Sudduth says. While it rains, the water level in the tanks fluctuates between the prescribed minimum and maximum levels.
The water in the tanks is used for the building's indoor landscaping. "Our lobby is about 25,000 square feet and has significant indoor landscaping," explains Shannon Westberg, general manager of the building. "We have an in-house horticulturist who uses the water from those tanks to water the interior landscape almost exclusively. Unfortunately, there is not enough water in there at any given time to handle our outdoor irrigation as well, but that's minimal because we're downtown."
The tanks are elevated approximately 3 feet off the ground and there is a hose connection on the piping, which allows the horticulturalist to attach a garden hose and use the weight of gravity to run water out of the tank system and into the storage vessel with a pump that he uses to water the landscaping.
Maintenance for the system is minimal, as intake for the pump is located at the bottom of the tank, and when the pump system pumps water from the tank system, it empties the tanks to a minimal level – this keeps sediment from building up inside. "What is pretty amazing is that the system went in place to stop flooding in the basement, and in turn has turned into an environmentally friendly LEED point for us," Westberg adds.
OSU Uses Harvested H2O
Oregon State University (OSU) also opted to install a rainwater reclamation system on its new Kelley Engineering Center (KEC), although the goals differed greatly from those of the Hurt Building. "The goals were to reduce water usage and the city sewer charges, which are assessed on the amount of water used," explains John Gremmels, senior project manager in Facilities Services at OSU. "We also got a LEED point for this system."
The system itself, and the uses for the reclaimed rainwater, are also more diverse. The conventional gutter system diverts rainwater into planters that contain native and drought-tolerant plants, which act as bio-filters for the rainwater, before sterilization, storage, and use inside the building. "Stormwater from the roof and the planters plumb through a filter under the plaza and into three 4,500-gallon tanks," he explains. "The water recirculates through a UV filter and is used in the toilets and urinals, which flush to the sanitary sewer."
Gremmels estimates the system saves 1-2 million gallons per year, or about $2,000-$4,000 in city charges since the building opened in 2005. However, he still calculates that the system has around a 20-year payback, "which means it doesn't really make sense except for LEED concerns."
Is Rainwater Realistic?
The feasibility of a rainwater harvesting system will depend on your water budget and the rainfall pattern in your area. "You have to look at where you are. It's very regional," says Ruck. "Seattle, WA, is going to get different rainfall patterns than Raleigh, NC. Look at your 30-year rainfall averages to determine a water budget and how much catchment area you need for your system. You have to look at the end use and how much water you need."
Installing an extensive system in an area that has relatively low rainfall may take too long to pay off for the system to be practical. However, installing a smaller system or an extensive system in an area with heavy rainfall may pay for itself in a much shorter, reasonable amount of time.
Ruck cites an example of a school in Raleigh, NC, that uses water collected from the gymnasium roof to flush toilets. "They have approximately 80,000 square feet of roof area, so for every inch of rain, they're going to get roughly 49,000 gallons of water," he says. "In North Carolina we average between 3 and 4 inches of rain per month, so that collection area of 80,000 square feet is shedding 150,000 gallons of water a month. This particular system has a 100,000-gallon capacity system, and at 2,000 students at 1.6 gallons per flush, 3 times per day, they're going through 10,000 gallons of water per school day. So if you look at the 10,000 gallons and divide that by $7 per 1,000 gallons, they're saving $10 per day." With those numbers, Ruck expects the ROI of the system to be seven to eight years.
Rainwater harvesting is becoming more widely accepted as companies, cities, and states strive to take advantage of a virtually free natural resource. "Water is like oil, in the sense that it's not getting any cheaper and they're not making any more of it; what we have is what we have," says Ruck. "Rainwater harvesting not only helps to control stormwater runoff, but also addresses the fact that water isn't getting any cheaper."
Kylie Wroblaski (firstname.lastname@example.org) is associate editor of BUILDINGS.