the advantages of rainwater collection:
Flexible system--easy to reconfigure,
expand, or in some cases, relocate.
Can be installed or expanded on a
'pay as you build' basis.
Reliable--eventually, you will have
water in your tanks!
Clean, and the water chemistry is
easy to manage.
Can be sized to the need at hand,
and integrated into new construction easily.
Relatively easy for owner/builder
to do with little help.
Excellent back up system.
Can easily be tied into well water
Can be put inside a barn, large garage,
or in a basement.
Water is still available if you have
no power, though at diminished pressure.
Pumps can run off solar or 12 volt
Tanks rarely freeze except in sustained
extreme cold due to their thermal mass.
Easy to tie into solar water system.
Most of the system is accessible,
rather than buried, so repairs are easy.
Few expensive components.
the disadvantages of rainwater collection:
Aesthetically intrusive - you have
to do something with big tanks.
May not meet local building code requirements
for primary water source for new construction
Requires more ground space than a
well for the storage tanks and pumping system
Requires a good sized roof
Roof materials and airborne pollutants
can pollute the rainwater
Gutters require constant maintenance