We're being encouraged to drink more water. And we're being encouraged (even subsidised) to put in rainwater tanks for household and drinking water. But what are the dangers? Acidity! Rainwater is naturally acidic. Low pH (acidic) water = dissolved copper from copper pipes. Copper is a poison! ....and the results of dissolving your copper pipes also equals paper-thin pipes that leak and burst! This is expensive and highly destructive, especially if the pipes are inside brick walls! Some bore waters have a naturally low pH. We've seen bore waters with a pH as low as 3.3! Yet actually MOST rainwater in Australia has a low pH, due to dissolved carbon dioxide in clean air and/or degrees of sulfur dioxide in polluted air. Read some of the following articles ( https://www.cmar.csiro.au/e-print/open/info98_1.html https://www.dar.csiro.au/information/urbanpollution.html https://www.ausetute.com.au/acidrain.html ) for further explanation. Never assume that this can't happen with rainwater. We commonly treat rainwaters with pH ranging between 5.0 and 6.5, and they all exhibit dissolved copper problems. See https://www.biofarmag.com.au/index.php?module=ContentExpress&func=display&ceid=59 and https://www.biofarmag.com.au/index.php?module=ContentExpress&func=display&ceid=51 for further information.