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"Twice Filtered"

The term “twice filtered” was introduced by The Helena, a LEED Gold certified building that in 2004 became the first large-scale residential project in New York City to offer comprehensive water filtration – supplied by BETTER WATERS.  

The “twice filtered” method – filtering water in two separate stages – is the most efficient means for a multi-residential or office building to provide sustainable filtration to replace bottled water.  It‘s also usually the best method for most single-family homes. Having “bottled” quality water for all purposes may be nice to imagine, but in most cases it’s impractical and unnecessary.

LEED CIR for the "twice filtered" design

Dividing the workload into two stages
Stage One, “point of entry"

At the main, particle filtration only. Whether the incoming flow is 15 or 400 or even thousands of gallons/minute (GPM), the principle is the same. An extremely fine yet practical filtration level at “point-of-entry” is about 10 microns.  (The threshold of visibility is 40 microns.) 

 New York City water, for example, has an exceptionally high turbidity level – close to the EPA’s maximum contaminant level (MCL) – caused mostly by the oxidation of dissolved manganese and iron as water travels from the source reservoirs through miles of pipe.  If you live in a NYC building without filtration, you probably notice periodic discoloration when you fill up a sink or bathtub.

Three major benefits of stage one filtration:
  • Water runs crystal clear throughout the building, kind of a nice touch when you’re taking a shower or bathing your baby in a property you just paid a million bucks for. (Also nice if you rent.)
  • As manganese and iron oxidize, they become strong discoloring agents.  Removing them from the domestic water supply prevents discoloration of bathroom and kitchen surfaces and fixtures, so a lot less cleaning formula ends up going down the drain.
  • The longevity of those secondary stage filters we talk about next is dramatically increased – on average by two or three times – because the coarse particulates that can quickly clog a submicron drinking water filter are removed ahead of time.
Next: Stage Two, "point-of-use"

Stage Two, “point of use”

If we are really going to reduce our reliance on bottled water, the drinking water filtration system that replaces bottled has to deliver equal or better than bottled.  At the same time, the filter cartridges have to last long enough that the system is easy to maintain. These two criteria alone eliminate most drinking water filters on the market from consideration.
The system is typically installed in the cabinet under the kitchen sink. Depending on the model selected, it can be installed directly in-line – all cold water from the kitchen tap will be filtered – or installed with a tee in the cold water line directing filtered water through a separate “glass filler” faucet.
A direct, in-line installation is a simpler install, which for a large-scale project can mean significant savings in labor and materials.  On the other hand, there are also advantages to separating filtered water from the cold, general purpose water at the kitchen sink.
Twice Filtered - Two Essential Factors
Water filtration is the answer to the growing environmental impact of bottled water, because the technology reconciles people’s desire for pure, safe drinking water with the imperative of reducing waste.
But the details matter.  For a system to be sustainable, it must (1) truly eliminate the need for bottled water and (2) have the least environmental impact.
Water Quality  People are not wrong to be wary of tap water.  A water filter that does not reduce to virtually non-existent levels the probable contaminants in tap water will not, at the end of the day, reduce dependence on bottled water - small refrigerator filters, or the types commonly available in stores, are essentially cosmetic.  If the object is to encourage people to break the bottled water habit, they must have in place a technology that offers water equal or superior to bottled.
Environmental impact   While the use of nearly any filtration system is better for the environment than using bottled water, systems that last longer will naturally have less environmental impact than those with filtration cartridges that need to be replaced more often. Generally speaking, the larger the filtration cartridge, the exponentially greater filter longevity (capacity) becomes. That’s because there is an exponential increase in the amount of water the filter can receive before it reaches its threshold of resistance – the point when it is holding so much particulate matter it becomes an impractical barrier to the flow of water - and must be replaced.


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Drinking Water Contaminants - info from the EPA site

Read about Drinking Water Contaminants from the EPA website

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Information Center

Information about water quality and related topics.  Media articles and environmental perspectives. Water Quality Reports from around the US.

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