The Water Efficiency Blogs

A article with good thoughts. The next step is to device inexpensive ways for filteration and clean storage systems to be handled by households &/or small businesses, to reduce pumping problems. Simple and inexpensive system is the key to adoption - in the US and primarily in developing countries.

The key here is cost effectiveness. Integrated, commercial or even residential scale systems are expensive to implement when scaled properly for the use objective. Expensive relative to what? Basically subsidized water. Your municipal water, without sewer charges typically costs less than 1 cent per gallon at the tap, purified to drinking water quality standards. Folks who study water cost models argue this cost reflects infrastructure maintenance and pumping costs only, but essentially no cost for the (finite) resource being provided. Until that changes, harvesting systems will always be considered expensive. The only way to understand the true cost, even relative to subsidized municipal water systems, is to know what the cost of centrally supplied water will be 5, 10 or 20 years from now. If that were known or reasonably projected, you could compare the amortized cost of the harvesting system install with the savings over those time periods to determine the breakeven point (factoring in some O+M). Fortunately even the EPA is on to this. Full-cost price modeling is a topic in their recently published "Guideline" for rainwater harvesting. A copy of the guide can be found at www.blog.rainwaterrecovery.com. It's a sign that things are indeed changing. The other factor is Utilization - the amount of otherwise domestic water the harvesting system offsets by being the 1st-use source at a facility. Given that as much as 50% of indoor use at many homes is for non-contact (i.e. non-potable) use, the potential here is enormous. Commercial installations are even more compelling. The key to optimum harvesting system performance is getting the storage volume (cistern size) right. Since the cistern is the system's most expensive component and the one with the largest impact on Utilization, its critical to know you've got this variable pegged. Using a monthly water budget analysis is a start, but is usually far to coarse to base such an important decision on. Our firm has over 100 systems in production - all of which we've designed - and over 1/2 of which we built under design/build contracts. Most designs we see by others use elementary sizing models which miss the optimum cistern size for the demand profile by 50%-100%. More information is available at rainwaterrecovery.com Lastly, beware of one-size-fits-all product offerings. In harvesting systems there is really no such thing. Again, determining the appropriate cistern size is the most critical piece, then incorporating site constraints (e.g. collection points and elevations, depth to rock and groundwater, site access issues, etc.) to arrive at the proper form-factor for the cistern. Deciding it should be pre-cast or FRP, or perhaps worse, a chain of smaller cisterns interconnected, before determining the primary criteria usually leads to unnecessary problems or low system performance. Have a good water day!

There already exists cost effective ways to clean the captured rainwater. There is a company,Rainwater Management Solutions, that offers complete rainwater haresting systems for both residential and commercial applications. They have installed a number of working systems. Their website is www.rainwatermanagement.com Also,one must realize that the pollutant loading of rainwater runoff from roof areas is much less in volume and complexity than wastewater. The principle pollutant sources are bird droppings and air borne particulates (i.e. dust). Therefore it should not difficult to design a biofiltration system that could operate in a solarium or atrium to clean the water sufficiently for it to be potable. The biggest expense will be in the regular sampling and testing needed to be assured that the water is potable, do to a lack of long term experience with such systems.