Rainwater Harvesting on Daufuskie
Capturing and using for domestic purposes the rainwater that naturally falls on Daufuskie will reduce our demand on the Floridan aquifer, while also helping to protect our rivers and marshes from excess stormwater runoff. Rainwater harvesting, through something as simple as a rain barrel, can, therefore, positively impact both water quality and quantity.
Rainwater Harvesting and Water Quantity
Daufuskie Island receives, on average, approximately 50 inches of rain annually. Some of that rainfall nourishes the native vegetation, some of that rainfall soaks down into the ground into the aquifers, and some of that water runs off the land and into wetlands, streams, marshes, and the rivers. Therefore, capturing the rainfall in rain barrels or cisterns for irrigation purposes, instead of using groundwater from the Floridan aquifer, represents an opportunity to significantly reduce per capita consumption of groundwater on Daufuskie Island.
Just how much water is 50 inches of rain annually? Consider this – 1.6 inches of rain falling over one square foot of area equates to one gallon of water. So, during the course of an average rainfall year on Daufuskie, 31 ¼ gallons of water will fall on one square foot.
If we were to make an assumption that the average house on Daufuskie will cover 1,000 square feet of land with a roof, we can then calculate the amount of water that could be harvested by redirecting the water to rain barrels or cisterns. The calculations are as follows:
Average gallons of rain per square foot 31.25
Average roof area per home 1,000 square feet
Average volume of roof runoff per home 31,250 gallons
With approximately 31,250 gallons of free rainwater available to the average Daufuskie Island home for non-potable uses such as irrigation, doesn't it seem wasteful to pay for water from a water provider to irrigate your landscaping?
Rainwater Harvesting and Water Quality
When your home on Daufuskie Island was built, previously undeveloped land that had been covered in native vegetation became covered with your house. What had previously been a pervious surface that allowed water to be gradually absorbed into the ground became an impervious surface that shed rainfall as quickly as it fell from the sky. The impact of the impervious surface is felt by the adjacent pervious surfaces, which may quickly become saturated and unable to absorb the extra runoff. The net impact is that water that would have been absorbed into the ground prior to the construction of your home may now flow into marshes and rivers.
This increased runoff poses problems for the water quality of our local waterways. It is not uncommon for oil or gasoline to be present in small quantities on the ground as a result of routine vehicle operations. These pollutants can be swept up by runoff and deposited in the local waterways, degrading quality.
Oddly enough, water quality is also degraded simply by the influx of too much freshwater. Our local estuarine environment evolved to accommodate the natural fluctuations in salinity that occur throughout the year. However, an increase in runoff due to more impervious surfaces can upset the salinity levels by putting more freshwater into the rivers than would normally occur.
Rainwater harvesting can help to preserve the water quality in our local waterways by reducing the impact that increased impervious surfaces have on runoff. When you store rainwater in your rain barrels or cistern, not only do you ensure that you have the water you need for irrigation, but you control the release of the water in a manner that allows the ground to absorb it gradually. Water that is absorbed gradually into the ground does not carry pollutants into the local waterways, and it does not upset the salinity levels of our rivers and streams.
Water is one of Daufuskie Island’s truly precious natural resources. The salty waters of the surrounding ocean and rivers have provided a bounty of food for thousands of years, and the stores of freshwater underground have provided drinking water during the same time. How we on Daufuskie manage our water resources now and in the future will determine whether or not future generations will be able to enjoy life on Daufuskie.
Where do we get our drinking water?
Chances are that when you turn on the water in your Daufuskie home, your water is coming from a well that taps into the Floridan Aquifer, one of the most productive aquifers in the world. Groundwater, or water that is provided via wells, is the preferred source of drinking water in the Southeastern US because there have historically been abundant supplies and the quality was good enough to not require treatment prior to human consumption. There are some homes on Daufuskie with shallow wells that do not reach deeply enough to tap into the Floridan Aquifer.
Is the Floridan Aquifer a sustainable source of drinking water?
It depends. The Floridan Aquifer naturally recharges when precipitation levels are high enough to allow water to seep back into the ground. When water is extracted from the aquifer at a rate faster than it is recharging, the pressure within the aquifer decreases and the aquifer then begins to shrink. So, it is possible to overdraft the Floridan Aquifer and create a situation where it is no longer a viable source of drinking water.
In fact, the Floridan Aquifer is already shrinking and has impacted the water supply options for neighboring Hilton Head Island. Due primarily to large water withdrawals in the Savannah area, the decrease in pressure has created weak points in the boundary of the aquifer, allowing salt water to intrude into areas that had previously been filled with potable water. This salt water intrusion has forced Hilton Head Island to shut down some of its large public water wells.
Could salt water intrusion threaten Daufuskie’s drinking water supply?
Yes. The United States Geological Service modeled the impact of groundwater pumping on saltwater intrusion of the Floridan aquifer and concluded that, based upon maintaining groundwater pumping levels experienced in 2000, the saltwater intrusion would continue to move from Hilton Head towards Savannah at a pace of approximately 350 feet annually at an increasing rate. While that pace of intrusion does not suggest an immediate threat to our water supply on Daufuskie, it does clearly demonstrate that our drinking water supply is not sustainable given the demands of our region.
Salt water intrusion into the Floridan Aquifer in the Hilton Head/Daufuskie area is being modeled by the Georgia DNR. The modeling report with the model and conclusions can be viewed in the web site: http//www1.gadnr.org/cws/. A steering committee has been formed to make recommendations for future actions consisting of people from the water districts from Georgia and South Carolina. Paul Vogel of the DI Conservancy is on this steering committee.
What Can We Do?
There are a number of good web sites on saving water and some of the best are by the EPA. One for solutions is http://water.epa.gov/action/thingstodo.cfm.
Learn about your personal consumption behavior. For those who live in the larger planned communities on Daufuskie, where water is provided by some sort of water system, the homes are equipped with a water meter that allows for monthly measurement of water usage, and billing for the water used. However, for those on Daufuskie who rely on personal or community wells, typically a meter has not been installed. Clearly, this makes measuring personal consumption quite difficult. For those homes, the Daufuskie Island Conservancy recommends purchasing a home water meter.
In terms of household water usage, the average four-person household in the United States consumes approximately 400 gallons of water per day, with approximately 70% of that consumption taking place inside the house and the remaining 30% associated with outdoor usage such as irrigation. In other words, the average person in the United States uses approximately 70 gallons of water each day at their home.
In her book, "Handbook of Water Use and Conservation", author Amy Vickers compiled data on water usage inside the home. Her research showed that the average US household used 69.3 gallons per person per day for inside uses, and that the usage was broken down into the following categories:
UseGallons per Capita Percentage of Total Daily Use
Other Domestic Uses
Assuming that conservation methods such as installing low-flow fixtures, exchanging newer, water efficient appliances and toilets, and repairing any leaks were implemented, Ms Vickers calculated that households could reduce their per person consumption by 35%, down to 45.2 gallons per person per day. The revised usage pattern would then resemble the following:
UseGallons per Capita Percentage of Total Daily Use
Other Domestic Uses
If you are building a new home on Daufuskie, or renovating an existing home, The Daufuskie Island Conservancy encourages you to select WaterSense labeled plumbing fixtures and appliances. WaterSense is an EPA-sponsored partnership program that seeks to protect the future of our nation's water supply by promoting water efficiency. Better yet, seek to have your entire home comply with WaterSense single-family home specifications. For more information about WaterSense labeled products, please go to the following link: http://www.epa.gov/WaterSense/products/index.html
What about outdoor water usage?
Of the 100 gallons of water per person per day consumed at the average US home, approximately 30 gallons is associated with outdoor water usage. By far the largest component of this water usage is irrigation associated with lawns and other landscaping components. There are some relatively simple steps that can be taken at your Daufuskie home to drastically reduce your average outdoor water usage.
First, consider landscaping with native plant species and/or plants that thrive under our natural climate.
Water, water everywhere but will we have enough to drink?
"It is a strong possibility within the next few decades that Daufuskie Island will have serious drinking water issues. Wisely using water is one of the best ways to protect drinking water sources for the future." This sobering message was delivered by Chuck Gorman, Director, Water Monitoring Assessment & Protection Division, DHEC at an educational event organized by the Daufuskie Island Conservancy on April 13, 2009. Water quality and conservation was the number one environmental concern identified by people who responded to the 2009 DIC survey. This prompted DIC President, Laura Winholt to invite experts to share information about DI's water source.
Where do we get our water from?
Alex Butler, Hydrogeologist, described that many people on DI get their drinking water from the Floridan aquifer.
An aquifer is an underground layer of water-bearing permeable rock or unconsolidated materials (gravel, sand, silt or clay) from which groundwater can be usefully extracted using a water well.
With development and high water demands, the pressure in the aquifer decreases which allows salt water to flow in. Hilton Head Island has already experienced saltwater intrusion and has recently installed a $1+ million reverse osmosis system as a solution to their water challenges.
How much water do we use?
Alex also shared some interesting statistics about water usage on DI. Members of the audience were surprised to learn that in one year, 100 million gallons of water are used. The average person in the U.S. uses 70 gallons of water a day. On DI the average is 258 gallons per day. (This number excludes water used to irrigate the golf courses.) A high volume of this water is for irrigation. It was reported at Haig Point that 69% of water usage is for irrigation by homeowners.
What do people with wells need to pay attention to?
People with shallow or old wells may get water from the superficial aquifer. Because this water source is so close to the surface, the quality of the water is variable. Water testing is encouraged. If you are interested in testing your well, Laura Winholt has testing kits available. The cost of a bacteria test is $20 and a metals test is $50. For the Residential Well Program, see www.scdhec.net for complete information. DI Conservancy is collecting private well water samples for bacteria and metals. Here are the steps:
#1 Pick up a water test kit from the Fire Station. The kit contains a sterile bottle, form 1309A and an instruction sheet.
#2 Collect the water sample on Sunday, May 17th at 6 p.m. and immediately take it to the lobby of the Fire Station and put it into the drop box. Samples over 30 hours old will not be tested. The box will be picked up at 7p.m.
#3 The water will be tested on Monday, May 18.
#4 The results will be mailed to each person with an invoice ($20 / bacteria and $50 / metals). DHEC may waive or reduce the fee based on the individual's ability to pay.
The speakers and people in the audience asked us to consider how we can be good stewards of our water supply. One simple way is to irrigate less. Check your water bill to see how many gallons of water pour through your irrigation system. The speakers recommended that DI develop a plan to handle drinking water shortages before there is a crisis.
How can we be good stewards of water?
We need to treat water as a precious resource.
Take the DIC water challenge – how much water can you save each day?
Turn off irrigation systems or use them less frequently.
Use drip irrigation for shrubs and trees to apply water directly to the roots where it's needed.
Frequently check outdoor taps and irrigation systems to ensure they are in good working order.
Water plants early in the morning or late at night to reduce evaporation.
Use a broom instead of a hose to clean your driveway – save 80 gallons.
Wash fruits and vegetables in a bowl of water rather than letting the tap run.
Turn off the water when brushing your teeth – save 4 gallons a minute.
Shorten your shower by a minute or two - save up to 150 gallons per month.
Run the washing machine only when you have a full load – save up to 600 gallons a month.
Simple things can make a big difference.
Written by: Sheila Cook for the DIC