sf wrote:
>
> On Thu, 05 Dec 2013 10:22:02 -0500, "Pete C." >
> wrote:
>
> >
> > sf wrote:
> > >
> > > On Thu, 05 Dec 2013 08:44:07 -0500, "Pete C." >
> > > wrote:
> > >
> > > >
> > > > Ed Pawlowski wrote:
> > > > >
> > > > > On 12/3/2013 2:52 PM, Helpful person wrote:
> > > > >
> > > > > >
> > > > > > Unfortunately the water where I live is horrible so I am forced to use bottled,.
> > > > > >
> > > > >
> > > > > Either an RO system or proper filters will pay for itself over bottled.
> > > > > You do have choices.
> > > >
> > > > The $150 or so under counter RO systems work very well and are very easy
> > > > to install.
> > >
> > > What is the "waste ratio" all about and why do the lower cost units
> > > have a higher one?
> >
> > The reverse osmosis membrane essentially passes only clean water, which
> > means that the contaminants stay on the input side of the filter. This
> > water with concentrated contaminants generally needs to be disposed of
> > as "reject water" to keep the crud from building up and preventing new
> > water to be filtered from getting to the RO membrane. Higher end units
> > have better designs to allow for less reject water and thus less water
> > consumption.
> >
> > A key thing to keep in mind is that the under sink RO systems only
> > produce up to ~10 gal/day of filtered water, and the reject water is
> > only produced in proportion to the filtered water produced. Thus if the
> > ratio of reject water to filtered water is 1:3 the unit only "wastes" up
> > to 3.3 gal/day of water, and if you only use 1 gal of filtered water in
> > a day it only wastes .3 gal of reject water.
> >
> > If you are particularly frugal that reject water can be collected for
> > other uses such as watering non-food plants or flushing toilets or
> > similar where the increased concentration of contaminants won't be an
> > issue. This would require some work on your part to do since such
> > reclamation setups aren't commercially available for a small home unit.
>
> Thanks, that could be a very expensive proposition considering the
> cost of city water these days and how it its increasing.

Not really, and it's an easily calculable expense. Your cost for
filtered water is the cost of the RO and pre filters divided by their
service life in gallons, plus the cost of the reject water for that many
gallons of filtered water. given the specifications for a particular
unit and the water cost it's easy to calculate the extra cost per gallon
of filtered water. It's likely in the range of $0.03-$0.05 per gallon.