A contractor recently asked me what kind of paybacks we see with rainwater harvesting. Some suppliers say that there is NO payback, and from what I've seen of their product, I would agree! But I'm seeing paybacks as short as 5 years, which is pretty good on equipment with a 20 year WARRANTY. The elements that make for fast payback are:
1. Lots of nonpotable demand. Cooling tower makeup and irrigation are best candidates. How much is the landscaping worth, if there's another total watering ban? In Atlanta, we've had 2 summers in the past 20 years where outside watering was totally banned. Can we assume a 10% annual likelihood in the future?
2. Minimal piping. Locate the tank close to the piping. Stay out from behind walls. Until rainwater is generally approved as a potable water source, we will have to steer clear of using it for toilet flushing when retrofitting. Just too much labor installing a second set of piping.
3. High water costs. Atlanta's are the highest in the country, and are expected to continue to rise at 5-10% per year for the foreseeable future.
4. High impervious surface charges. Atlanta doesn't have these YET, but Gwinnett, Dekalb, East Point, and others do.
5. High sewage costs. Some areas allow you to eliminate the sewage costs for cooling towers and irrigation, and some don't. Dekalb no longer offers separate irrigation meters. . . they need the money!
6. Use the right equipment. Above ground tanks are now $1-2/ gallon. Below ground tanks can run $4/gallon or more, depending on installation. How much granite is in the ground in Atlanta???
Yaskawa IQ Drives replace control panels. No treatment for cooling tower or irrigation. The submersible well pump in a sleeve design has been replaced with rainwater-specific submersible pumps. Piping to the tank can now go through the base, eliminating the need for heat tracing pipes.
7. Does the owner value environmental responsibility? The above-ground tanks show customers and employees a conservation mindset. It might translate into more sales or motivated employees.
Have you evaluated a project and found the payback period to be excessive? Send us the numbers, we love to value engineer.