Dear Solar Guy,

        Recently I heard a rumor that a big problem with solar water heaters
is scaling due to water hardness.   I don't want to put in a water heater
that gives me a lot of problems.   Is this really something to be concerned
about ?  

 M.J. in Sweetwater.

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Dear J.B.,

        What you heard was likely true, but seems to be associated with
locations which exhibit high water hardness and/or pH.  For example, Austin
water tends to exhibit significant scaling, and its water has an unusual
chemistry due to the method of water treatment.  It's water pH is around 10,
which is abnormally high, and tends to result in calcium carbonate formation
(scale).  It appears the water treatment in Austin will be modified to
reduce this problem, not just for solar water heating applications but for
the water distribution system in general.  Also, it is likely that scaling
will be more severe for well water than for municipal water.

        So, my advice to you is to check your local water chemistry from
your local water district and if it is below about 8.5 scaling is not as
likely to be a major concern.  
 The Solar Guy.