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Category Archives: Water use reduction

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Keeping Harvested Rainwater Safe

We are often asked about the necessity of sanitizing harvested water before it is used. After all, when we are talking about clean rainwater coming from a roof, how much risk is there that there will be harmful pathogens in the water? Some remind us that cultures throughout the world regularly harvest – and drink – untreated rooftop rainwater. So if we are using it for non-potable applications, why bother to go through the cost (and maintenance) of adding a sanitizer like chlorine or ultra-violet? (Most understand and can agree that greywater (gray water) has all kinds of potential pathogens, so of course we should sanitize that source.) But what about rainwater

Here’s how we respond to that question. We think the risk that someone will get sick flushing a toilet or watering a lawn with with “raw” rainwater is pretty low. And if the harvester is a homeowner, and the storage cistern is a rain barrel under the downspout, then we agree that going through a sanitation step would be silly. But the systems we design are for commercial and institutional buildings; public buildings. Now the potential for a public health risk goes up dramatically, as does the standard for proper treatment. What could be in rooftop rainwater that could hurt someone? Bacteria, bird flu virus, and other pathogens. An article in this week’s Chicago Tribune underscores that risk – Two Dead From Legionnaire’s Bacteria – Chicago . Legionnaires is caused by a bacteria that grows in warm water, and can be transmitted to humans breathing a sprayed mist from the source (think sprinkler or spray from a flushing toilet).

Legionnaires and other similar health risks from rainwater are very unusual and the risk is low. But who wants to take that risk, especially when we have simple, proven methods for making that risk essentially zero? For a typical commercial system, the cost of adding a chlorination or U.V. step usually adds only 5-10% to to the cost of the system.

Which sanitation method is best? Chlorine and ultra violet are the two most common sanitation methods for harvested water and greywater harvesting. The advantage of chlorine is that once it has disinfected the water, it has a measurable “residual” value that we can use to confirm that the water is properly treated. We can manage that residual to about 5 parts per million, which is about the level in your municipal water supply. And that residual level of chlorine continues to protect the water downstream in pipes, tanks and toilets. Of course, chlorine is a consumable, and these systems need more added every few weeks. Ultra Violet is a great sanitizer in that it is chemical free (green!) and the bulbs last 10,000 hours – so the system can run for 1-3 years without maintenance. But we can’t confirm that UV has done its job correctly unless we send the water out to a lab for testing. And there is no “residual” value for UV, so once the sterile water leaves the UV system, it can become contaminated again downstream.


In addition to all that, we take pride in the systems we design. We want to sell and support rainwater and greywater harvesting systems that do what they are supposed to do: Make a meaningful impact on the water savings for a building. And we want those systems to deliver clean, safe water with minimal maintenance. So we bristle when we are asked to supply a system without a sanitation step – and if we can’t convince the owner otherwise, we often let someone else do the design and build. Better to leave someone else to the risk and concerns of a system that is not properly designed.

For more information on rainwater harvesting sanitation, visit our site: 10.0.0.83/wahaso

Offsetting Water Shortages with Grey Water Harvesting

It happens every summer. We grow to expect it. When the summer heat scorches our lawns, every town in America begins its yearly water ban, limiting the amount of water used and sometimes banning water activity outright, save for daily necessities. It seems so regular that it is hard to believe there was once a time where this didn’t occur. Yet a solution does exist: a process known as grey water recycling.

Grey Water: A New Solution to an Old Problem

Grey water is simply defined as water that has been “gently used” in sinks, baths and showers. It does not come from toilets or water with food waste, and yet it can make up eighty percent of the waste water generated by a single household. With a simple grey water harvesting system this useful water can be cleaned and sanitized for non-potable reuse such as irrigation. Grey water harvesting alone could potentially save a community thousands of gallons of drinking water for consumption, rather than wasting it on watering lawns.

From Grey to Clear: Making Recycled Water Clean and Safe

While grey water is an excellent source of outdoor watering and can also be used indoors for flushing toilets. However, regardless of the intended use, the water must be clean and safe before it can be exposed to the public. The process of reusing grey water for both irrigation and toilet flushing starts with harvesting the grey water and sending it through multiple filters to remove particulates. The water is then sanitized in order to ensure it is safe for public use. These precautions are necessary whether it is a small residential system, or a large-scale commercial system such as those designed by Water Harvesting Solutions (Wahaso).

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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