The only reason one should use distilled water in their coolant mixture
is because their well is so hard or has high levels of calcium, or
sulphur or who knows what.
Us city folk, don't have that problem,and regular tap water is just
fine.
Now the reason, and the only reason that one should change their anti
freeze on a annual, or bi annual basis is because the DCA level of the
ethylene glycol mixture starts to drop, causing a high electrolysis
problem between dissimilar metals in your engine.
Consider this;
The DCA level is like a coating inside your engine to prevent cavitation
from happening, and corroding the heck out of the engines internals.
Or in some cases, like in a diesel engine where there is a cast iron
block and steel cylinder liners, if the DCA is low, the coolant will eat
at hot spots on the liners and create holes in the liners and cause
compression leaks, or coolant leaks into the combustion chamber.
Also there is another factor to consider.
The correct DCA levels are like a proper PH balance, not to acidic, not
to alkaline, and this is where the Water Wetter comes in.
It is a alkaline additive to prevent, or help the coolant from going
acidic, and eating the internals of your engine.
There is  litmus paper test to determine where your coolant stands, as
far as correct DCA level, and I think this is a important consideration,
if your interested in extending the longevity of your engine.

Hatsa Lavista,

Terry

85 GL