Rising water prices, watering restrictions, drought, political confrontations over water rights and water shortages are just a few of the complicated factors that have landscape designers, home owners and business owners searching to find alternate, sustainable water sources for irrigation and domestic use. The search for a “new” water source has led many to re-discover water harvesting. Water harvesting is an ancient practice that is currently experiencing a strong revival in the United States and already enjoys widespread acceptance in many countries around the globe.
Water harvesting is the practice of collecting rainwater from roof tops, condensate from HVAC systems and, increasingly, stormwater from landscaped and impervious surfaces in a tank or cistern, and then pumping the water out to meet irrigation or domestic demand.
A properly designed and installed water harvesting system can provide safe and reliable water for the life of the system. The vessel used to store the harvested water is often the largest and most expensive component of the water harvesting system, therefore choosing the right storage option is critical for the success of a system.
This article will compare and contrast the different storage options available for water harvesting systems.
The first option to consider when selecting a water harvesting storage tank is whether the system will be an above ground or below ground system.
Above ground storage tanks are usually the most economical to install, as no excavation and backfill are required for the installation. In addition, above ground tanks are generally more economical to manufacture since they are not manufactured to handle the structural loads below ground cisterns are exposed to.
However, due to freezing temperatures, above ground tanks are best suited to warmer weather climates in which the water can be stored and used year round without the likelihood of freezing. One of the distinct challenges of using above ground tanks can be the conveyance of the water to the tank.
Collecting rainwater from rooftops can be made simple by locating the tank near a downspout. However, if it is necessary to collect off of multiple downspouts, routing the conveyance piping from the downspouts to the tank can be difficult and unsightly. The two most common types of above ground storage tanks are plastic (HDPE) and corrugated steel.
Most above ground plastic tanks can be purchased for 35 cents to 65 cents per gallon prior to shipping and installation costs. It is important to determine where the tank is manufactured in relation to the project location and choose a tank that is manufactured as close to the project site as possible.
In some instances, tank shipping costs can exceed the actual cost of the tank. Plastic tanks come in sizes ranging from 55 gallons to 12,000 gallons while corrugated steel tanks come in sizes ranging from 500 to 500,000 gallons. The installation benefits and challenges for corrugated steel tanks mirror that of above ground plastic tanks.
Corrugated steel tank prices vary widely in price, starting at 45 cents per gallon for large capacity tanks and going up to $3 per gallon for a smaller tank prior to shipping and installation costs. Corrugated steel tanks are made up of multiple components which include, the corrugated steel panels, the liner that holds the water, tank ladders, and fittings to name a few. In addition, most corrugated steel tanks must be assembled on-site which can contribute to higher labor costs.
Many commercial and residential projects utilize below ground cisterns for a variety of reasons, and cisterns come with their own distinct set of benefits and challenges. When project real estate is at a premium, burying a cistern is a wonderful way to preserve space above ground, while also keeping the rainwater cistern “out-of-sight-out-of-mind.” Additionally, most below ground cisterns can be buried deep enough so that the water level in the tank is below the frost line, which greatly reduces the time and effort needed to winterize the system.
Conveying water to below ground cisterns is also simplified due to the fact there is generally a large vertical distance between the downspouts and the inlet of the cistern, allowing plenty of room for gravity to pull the water into the cistern. The most common cisterns are manufactured out of plastic which can include polyethylene, polypropylene, or fiberglass.
The largest plastic cistern that is mass manufactured and available in the United States is 2,650 gallons, however the most common size is 1,700 gallons. Most 1,700 gallon plastic tanks are modular, so that multiple tanks can be linked together for overall capacities much larger than 1,700 gallons. Fiberglass cisterns are made-to-order for specific commercial applications, and cost a great deal more than mass manufactured plastic tanks.
Below ground cisterns can cost approximately $1 to $2.50 per gallon prior to shipping costs and installation costs, while fiberglass cisterns can cost $1.75 to $3.50 per gallon prior to shipping and installation costs. Installation costs for below ground cisterns are higher due to the additional cost of excavation and backfill, as well as higher initial tank cost.
Each water harvesting installation comes with its own set of challenges. Which type, size, and construction material of the tank or cistern is best for each project varies based on the project.
For the best results vist www.arcsa.org to find an ARCSA Accredited Professional.
The author is VP of sales for RainHarvest Systems and director for ARCSA.
Learn how one contractor practices and sells rainwater harvesting in our September Water Works newsletter at bit.ly/rainwaterharvest.