Re: [VAL] Re: grey water disposal

["Craig C." <craigcar@xxxxxxxxxx>]

Dr. G.,

>>As far as I can tell, sanitarians aren't so worried about true gray water.
But they tend to think dish water is black water because it can have
uncooked food, especially meat, in it that can carry bacteria.

Very true!  The primary role of water treatment is to protect public health
(from pathogens), another objective is to protect public waters.  Consider
that bacteria (non-pathogenic (good) bacteria) will break down organic
components in gray water.  If gray water containing a high organic component
gets dumped into a body of water bacteria will thrive, and in the process of
consuming organics will also consume some of the oxygen in that body of
water.  This will result in degradation of the water (potentially resulting
in fish kills, etc.).

Mechanical wastewater treatment facilities are built to handle gray water.
I suspect septic systems are also built for gray water, but the total volume
of water would be limited.


>>There would have to be a way to add fresh water to the gray water tank in
the home for the occasions when there wasn't enough gray water stored to
flush the toilet(s) and that is a possible cross connection.

Just a note concerning cross connections.  When a cross connection is
required, the most trustworthy way to prevent backflow is by using an "air
gap".  An air gap is created when a downstream receptacle tank's overflow
level is lower than its supply outlet.  The best example of an air gap is a
household sink.  The faucet outlet is at a higher elevation than the sink's
overflow level.  (Technically, the supply outlet must be at least 2 times
its inside diameter above the receptacle's overflow).

Please don't dangle a section of hose from your laundry faucet into the
laundry sink.  Although backflow is highly unlikely, it can happen (and has
happened).

The best mechanical backflow prevention is a "reduced pressure zone backflow
preventer" (RPZ valve). An RPZ consists of a couple of spring loaded check
valves and a pressure regulated relief valve.  RPZ valves are highly
dependable but must be maintained ... as with all mechanical devices, an RPZ
can fail.

Craig