Rainwater Vessels: the good, the bad and the ugly
Good on you for deciding to capture and reuse rainwater and take a load off city systems! Saving water, saving “watergy”- the energy to used to push city water around the grid – and unloading the stormwater system downstream are just some of the benefits of rainwater harvesting which contribute to your karmic wellbeing and your water use bottom line.
Just as important in the green scheme of things, but often far less considered, is the vessel you choose for collection. “Green” credentials and contributory LEED points vary hugely between rain barrels, cisterns (also known as tanks) and other rain storage vessels. Like most consumer products, a cheap $/gallon price is not often the indicator of value or best sustainable practice. Just as the BPA debate has remodeled the drinking bottle landscape, a reconsideration of the material makeup and lifespan of rain-holding vessels is bound to shake up rainwater harvesting.
PVC bladders are an unquestioned under-house rain storage solution in Australia, yet many European countries and US cities have banned PVC for its severe end of life repercussions. The toxic dioxins released when PVC is produced or burned are suspected carcinogens thought to also bio-accumulate and cause long-term harm to animals and humans.
THE GOOD - saves space, cheaper freight
THE BAD - puncture or rodent incursion, stands are easily destabilized, some serious end of life issues
THE UGLY – The US Green Building Council states that “PVC (is) consistently among the worst materials for human health impacts…” and is considering a LEED credit for avoiding PVC.
LEED status- So a future point for NOT using PVC! Although you may theoretically achieve the two rainwater harvesting LEED points, city laws and possible upcoming LEED changes would suggest that other materials are a better choice for your rain containment.
Steel cisterns - corrugated or straight-walled –will feature a food grade bladder or bonded polymer lining unless they are made of stainless steel. Many steel cisterns larger than 9ft wide have a PVC or stainless steel center prop for additional support. Although steel cisterns have high embedded energy and water costs, some of these can be offset by recycling the steel at the end of its life. A stainless steel cistern is fully recyclable, whilst a lined steel cistern would need to have the bonded layer removed an thus is not technically 100% recyclable.
THE GOOD- large capacity, recyclable, wide range of shapes including slimmer profiles, wide range of colors, good in bushfire, repairable
THE BAD – can corrode, cannot be moved without potentially compromising its structure, radii constraints mean a steel cistern is never truly “slim”
THE UGLY – all depends on your aesthetic
LEED status – 2 contributory points for the rainwater harvesting and a possible point if the design is modular or otherwise innovative
Concrete cisterns contain up to 50% steel content, making their environmental footprint a chunky one and making recycling of both steel and cement a harder task. Heavier to handle and transport, concrete cisterns come into their own with sheer capacity and with their ability to handle bushfire. Although they are weightier, the anticipated lifespan of a concrete cistern is still 20 years, the same design life as a high quality plastic or steel cistern.
THE GOOD – robust, structurally useful, can withstand fire, no internal bladder, keeps water cooler than other above ground rainwater vessel options
THE BAD – can crack and corrode over time, heavy, unwieldy to handle and install, large environmental footprint, difficult to separate materials for recycling at end of life
THE UGLY – precast concrete has a monolithic, industrial look which you either need to work the architecture with, or hide.
LEED status – 2 contributory points for rainwater harvesting, possibly an extra if you can work the cistern into a design to harness the thermal mass.
And finally, plastic cisterns. Usually made of polyethylene which is petroleum-based, the sustainability of a plastic cistern ranges enormously from blow-moulded recycled food barrels with a working life of less than three years to robust ¼ inch walled rotationally molded cisterns designed with inbuilt UV stability for 20 years or more of useful life. Unlike Australia the USA does not regulate that rainwater tanks must be made of “virgin” food grade material, so many barrels and cisterns use recycled content which is “greener” upfront, but can heavily reduce the lifespan of a vessel. Reusing food grade barrels for example requires that the vessels are emptied and bleached every year, negating the reuse benefit with the requirement for chemical treatment. Other plastic vessels are so robust that they are designed to be reused several times over their life. Theoretically polyethylene is recyclable at the end of its life but the jury is out on whether UV light renders 20-year-old plastic recyclable or not.
THE GOOD – lots of choice in shape and function, durability (some models), slim lines (depends on design), integrated color and inbuilt UV stabilization, easy to install (the smaller ones)
THE BAD – inferior quality makes many of the lower cost barrels next year’s landfill, thin-walled designs prone to puncture
THE UGLY – plastic vessels not made with UV stabilization will need to be painted regularly, algae will flourish in barrels with open tops, requiring yearly chemical cleaning
LEED status – from a basic 2 points for rainwater harvesting up to 8 contributory points if the vessel has innovative features and the potential for reuse. Rainwater HOG modular tanks, shown above in black and yellow on a school building, have been known to garner 9 contributory LEED points under LEED for New Homes.
The slew of rain-holding solutions on the market offers a wealth of choice for those who wish to collect and reuse rainwater. Look for long life, robust, durable, UV resistant materials, and if possible look for something you are able to add to or reconfigure as your circumstances and water needs change. Think about how you choose the other essential appliances in your home and apply it to the purchase of your rainwater solution. As rainwater collection and reuse becomes the status quo across the USA those who take the time to navigate their rainwater vessel options will discover that the simplicity of rainwater capture in an appropriately sustainable cistern is a reward for life.
Sally Dominguez is an award-winning inventor, a published architect and an educator in sustainable design. Sally judges invention on ABC TV’s New Inventors and writes for a number of Australian publications on a range of sustainable design and material issues ranging from offgassing in vehicle interiors to green roof options and cardboard structures. See and read her work at www.beautifulusefulgreen.com