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Category Archives: Rainwater harvesting

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Harvest Greywater or Rainwater?

By John Bauer, Wahaso President

We find that there is a lot of confusion out there about greywater, (also called gray water and graywater), and rainwater usage. Which system is the best for a particular use? The usual assumption is that a greywater system, which must filter and sanitize water from showers and sinks, will be more expensive than a rainwater system. This may or may not be true, depending on your situation.

Generally, we find that a rainwater system makes the most sense when the following conditions apply for a property:

— The building is already existing, so it is economically unfeasible to separate the existing waste streams from the toilet, showers and sinks to capture greywater.

— The water use requires a very clean source with little dissolved solids – for cooling tower make-up, washer rinse or vehicle washing.

— There is an abundant source of rainwater in the area so that the storage size can be minimized.

— There is an abundant source of rainwater in the area so that the storage size can be minimized.

Greywater systems are often a better choice when these conditions exist:

— The building houses residents, so there is ample supply of greywater from showers and sinks.

— The primary uses of the harvested water will be toilet flushing and irrigation. Greywater is an excellent source for these uses.

— The building plumbing has not yet been completed so there is time to change the layout to capture shower and sink water separately from the toilet black water.

— The property is located in an arid part of the country that gets little or very seasonal rainfall.

If greywater is an option for your property – that’s good news. Unlike rainwater supply that is highly dependent on local rain events, greywater is a very reliable source, tied directly to building usage. Residents flushing toilets are also showering and washing their hands.

And while a greywater processing skid is somewhat more expensive than a rainwater system, the reliable source of greywater means that we usually only need to store a few hundred gallons of processed water at a time. That saves a tremendous amount of the cost and space requirements associated with a large rainwater system. A typical commercial rainwater system can require tens of thousands of gallons of cistern storage.

The net result is that a greywater system can predictably save more municipal water for a lower total system cost than a rainwater system. The one caveat here is the added cost of running a separate waste line in a building to capture the greywater for harvesting. Depending on the plumbing layout for a building, this cost can be relatively insignificant or a sizable investment.

And we should note that a greywater system will need a bit more maintenance than a simple rainwater system. Greywater sanitation requires the addition of chlorine, and there is additional filter maintenance. But these maintenance needs are typical of the many systems in a commercial building and require no special skills or training.

Our best advice about whether rainwater or greywater harvesting is right for you is to have you talk with us at Wahaso. We can help you evaluate the feasibility and cost considerations for both options as they relate to your unique building. Please contact Wahaso. And you can learn more about greywater harvesting and rainwater harvesting by visiting our website.

Add Water Harvesting to Your LEED Project to Achieve Gold & Platinum Levels

Many of our projects at Water Harvesting Solutions involve clients who are pursuing Leadership in Energy and Environmental Design (LEED) certification. This program, developed by the U.S. Green Building Council, provides an independent, third party evaluation of a building to determine if it meets optimum performance in five areas:

  • Sustainable site development
  • Water savings
  • Energy efficiency
  • Material selection
  • Environmental quality

Each performance area is assigned a set number of points which are accrued through meeting various criteria. These points are added up to determine if the building has achieved LEED certification. To certify a new building as “green” requires 40-49 points. More points are required to achieve the higher certification levels of Silver (50-59 points), Gold (60-79 points) and Platinum (80 points or more). Those higher certification levels almost certainly must include achievements in categories related to water conservation.

The water efficiency goals of the LEED program encourage smart water use both inside and outside of the building and can provide up to 12 possible points toward certification. In the area of Water Savings points can be accumulated in the following categories: 1) water efficient landscaping, 2) innovative wastewater technology and 3) water use reduction.

Harvested water can be a key component to obtaining LEED water savings points. For example, using captured rainwater or greywater for irrigation can provide points for the “water efficient landscaping” category. A 50% reduction of potable water for landscaping is worth two LEED points and a 100% reduction is worth four points. Water harvesting can also be used to gain two points in the “innovative wastewater technology” category. Reusing rainwater and greywater not only helps to reduce potable water consumption, but it also reduces the amount of water sent into the municipal storm system. Finally, up to four points can be awarded for overall water use reduction (irrigation is not included since it has a dedicated category.) A baseline for water usage is calculated for the building and the amount of points received corresponds to the amount of water saved:

  • 30% reduction from baseline = two points
  • 35% reduction from baseline = three points
  • 40% reduction from baseline = four points

Additionally, water harvesting can earn points in the area of Sustainable Site Development. Harvesting stormwater for reuse can earn one point for minimizing run-off and one point for reducing the amount of contaminants that enter the storm system.

Our most efficient systems often capture multiple sources of on-site water for multiple uses. So a single system might capture rainwater, greywater and condensate to flush toilets and irrigate landscaping, saving as much as 90% of the total municipal water an office building would otherwise use. These systems can earn points from all four categories and help boost a project into the Gold or Platinum point levels.
The benefits of LEED certification are both environmental and financial. Not only does reducing water consumption help to conserve a vital resource, but it also reduces costs for municipal water use and stormwater management. LEED certification is also shown to increase a property’s resale value, making the investment in a water harvesting system a winning proposition.

Kim Seay

Marketing Manager

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