Re: Reverse Osmosis Redux

[Pete Johnson <petej@wordsanddeeds.com>]

Rusty Witek writes:

>Does the gpd number refer to the output of processed water or to the
>pre-R/O'ed water?  (The point of this is to ask what size unit would be 
>best for, say, biweekly water changes for a 20 gal. and a 45?)

The gpd number is the amount of good water the unit produces each day. If 
you do 20% water changes on those tanks biweekly, you need only 26 
gallons of water a week, which a 4 gpd unit could theoretically cover. 
But get at least 10-15 gpd. Higher output units produce a lower ratio of 
waste water, and they give you more flexibility for emergency water 
changes (and tanks which spawn more tanks).

>How and where does one set up an R/O unit?  I understand that there needs
>to be a water source (!), but do you also need a large holding unit of
>some kind?

You need a water source, storage for the good water and an outlet for the 
waste water. The source is a faucet, a hose or a dedicated bit of 
plumbing. Trash cans will work for storing good water and waste water, 
though the (typical) 6:1 ratio of waste water to good water demands 
multiple trash cans for the waste, or else a method of sending it to the 
garden or the drain. It's often most convenient to set up an R/O unit in 
a back yard, if you have one. As others have mentioned, R/O units are 
most efficient with warmish water (over 65F) and the membrane won't 
survive freezing, so indoors is good if you have an appropriate space.

>(The R/O units in the catalogues look basically like a pair of
>scuba tanks, so I assume that when they say something like 24 gals. a day
>that the unit itself doesn't hold that water.)

They're water filter housings, about 16 inches tall by 4 inches in 
diameter and they offer only momentary guest facilities for the water 
passing through.

>Household approval for such a unit will depend less on "How much will it
>cost?" than on "Where will you put it?," "Will it be in the way?," and "I
>won't have to look at it, will I?"  :-)

In most states, R/O units are valid grounds for divorce. :-)


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        If wishes were fishes we'd all have ponds

Pete Johnson  /  San Jose, CA  /  petej@wordsanddeeds.com
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