Re: [VAL] Cleaning water tank

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

Phil,

Perhaps there are chemists, biologists or medical experts that can give a
better answer, but here's my best shot at it.

Short answer:
flush, disinfect, flush

1-Clean the tank, pipes, pump and valves to the best of your ability (scrub
where possible, soak in chlorine solution where possible).
2-Flush using potable water from a disinfected public water supply.
3-Disinfect using a chlorine solution (Concentration and time of your
choice, strong enough to kill pathogens but not so strong it damages valve
and pump parts.  See the technical stuff below for an idea about
concentration.)
4-Flush, flush, flush  then flush some more (using disinfected water from a
public water supply).
5-Always use (and regularly turnover) water from a public water supply.
(Public water supplies maintain a .2 ppm residual of free chlorine or a 1.0
ppm residual of combined chlorine in all parts of the water distribution
system.  Free chlorine is roughly 100 times more effective than is combined
chlorine.)  Watch out for water from campgrounds in remote areas ... may not
be subject to rules and regulations of a public water supply.


Longer (technical) answer:

One of the parts of my life I'm happy to have government involved in, is in
protection of public water supplies. Unlike some other parts of the world,
when illness from waterborne disease happens it makes huge headlines.  The
EPA sets standards and most states have a primacy agency to enforce the EPA
rules (and may set more stringent standards).


When a public water supply brings a new water main or storage reservoir
online these are the rules.  [NOT complete, MY summary extracted from the
Minnesota Water Works Operations Manual]:

The disinfection procedure consists of three operations: preliminary
flushing, chlorination and final flushing and testing.  Preliminary flushing
is done prior to every chemical disinfection.  The only disinfecting agents
in general use for water mains are chlorine compounds [this is due to cost,
effectiveness and because chlorine provides a residual for continued
protection].  The chlorine solution should be no less than 50 parts per
million (ppm).  The chlorinated water should be held in the main for at
least 24 hours and must have a 10 ppm FREE chlorine residual at the end of
the 24 hour period.  Treated water should stand in the pipe at least 24
hours, valves should be operated.  Circumstances may preclude a 24-hour
retention.  In these cases the chlorine concentration may be increased and
the retention time reduced.  For example a 100 ppm concentration could be
used for 12 hours [200 ppm for 6 hours].


HOW MUCH? (be sure to check my math)
-The most readily available source of chlorine is sodium hypochlorate
(liquid bleach)
-Most household bleach has a 5.25% concentration (check the label).
-A 5.25% solution of liquid bleach = 52,500 ppm.  (100% = 1,000,000 ppm)
-Therefore, mixing 1% bleach and 99% water provides a 525 ppm solution.
-1 2/3 cups of bleach in 10 gallons of water is a 1%/99% mix.

PROBLEMS:
Stuff in water (and growing in your tank) consumes chlorine.  Ammonia and
organics react with free chlorine to produce combined chlorine.  So without
the proper testing equipment you won't know if you have maintained a 10 ppm
free residual.  Also, most of us don't have bacteriological testing
equipment to check water quality when we're done.

Hope this helps and isn't just confusing.

Craig