Rainwater harvesting has been revolutionized by new technology and increasing concerns about global water security. In a rainwater harvesting system where water savings are the goal, a thorough analysis and design is a must; without it, rainwater harvesting systems tend to get either simplified or over-engineered.
An analysis will yield a hydrological model for the property in question, which is essentially an account of the water-in and water-out of a complete system. With the goal of water savings in mind, it is important to get an accurate picture of water usage estimates.
Without figures like water bills, it is nearly impossible to accurately build a model, and a miscalculation of just a couple hundred liters per day can drastically change the efficiency of the system. With these figures, a daily water usage estimate is possible. This calculation also provides a volume of void space in the water storage container, which will be used to calculate how much rain could be harvested on any given day, then determine the quantity of water entering the system.
In March 2016, a customer building a new family home on a rural property near Caron, SK, Canada, approached Cleanflo to design and install a rainwater harvesting system and a septic system. The home’s roof area was nearly 3,400 sq ft, and the customer wanted to collect from the entire area. Given that this project was a new build, the customer provided water bills from their existing residence, and their water usage was likely to remain relatively stable. The estimate was 404 liters per day in the winter and 893 liters per day in the summer, which is about 200 cu meters of water annually. This would serve as the basis for water-out when generating a hydrological model.
With the calculations completed and the optimized hydrological model in hand, the home could collect enough rainwater to supply approximately 76 cu meters, or about 37%, of their annual water demands. To compare, the alternative means of getting water is hauling. This costs approximately $0.03 to $0.05 per liter, which would cost approximately $6,000 to $10,000 per year.
Comparatively, the mains water in Regina, SK, Canada, is sold at a rate of $3.25 per cu meter, or 1/10th the cost of hauling water. In other words, by harvesting rainwater, the customer could save $2,200 to $3,700 annually. With a price tag of $20,000 on the complete rainwater harvesting system, including the 3,500-imperial-gal cistern, pump, treatment system, pre-filter, floating filter, and tank level monitor, the customer could expect to see a payback period of six to nine years for the entire system. However, because this customer is required to purchase a cistern in any case, the expected payback period of only the rainwater harvesting equipment is three to five years.
Value of Reuse
In 2017, Saskatchewan set a record for the driest July in 130 years and experienced an 100-year rainfall event. Despite being in one of the driest areas of the province, the system saved the home approximately $1,400 in 2017. If this were the new normal, the payback period would extend to eight years for the rainwater harvesting equipment and up to 15 years for the entire system.
Rainwater is a reliable and inexpensive source of clean high-quality water ideal for every use. Rainwater harvesting is not a process or a product, but a revolutionary source of water.
Originally Published in Stormwater Solutions