every time I return to the US, I have my doctor run blood work on my self and wife.

Blood tests here work just fine. . .

I am sure they do. But my insurance is in the US and I pay nothing out of pocket there.

> Rainwater like all soft water is fairly pure and therefore acidic and corrosive.

Sorry, but NO!

From Wickipedia:

"Because it has a pH of 7, water is considered to be neutral. It is neither an acid nor a base, but is the reference point for acids and bases."

In other words, water is neutral. In fact it is the definition of neutral.

Sorry you are wrong, I am an expert with 50 years experience in the water treatment industry. Clearly you are a layman with no experience, as you had to resort to Wikipedia to get information that you did not even understand. Uncontaminated rain water generally has a pH of 5.6pH and can be as low as 3.0pH (Acid Rain) or lower. The acidity of rainwater is caused by the take up of CO2 from the atmosphere which reacts with the water to form Carbonic Acid, and also Sulphur Dioxide which reacts and forms Sulphuric Acid. I think we are all aware of the atmospheric pollution caused by burning of rice paddies and forestry that we suffer from in Thailand, that leads to the rain water being acidic.

In my 50 years of working with reclaimed and recycled water, I have seen many galvanised tanks corroded away by customers wishing to use rainwater for make up water for their water recycling plants. I have seen untreated concrete gradually dissolve. Also I have seen car owners in the days of metal radiators, use rainwater or distilled water in their radiators only to have the radiators spring leaks like a colander within 6 months. If water has no impurities then nature wants the water to dissolve materials such as concrete so that it reaches an optimum hardness of around 150mg/l. One reason to be careful using R.O. water.

I've been drinking rainwater here for over 15 years with nary a stomach bug.

There is no pathogen in rainwater itself. However, in the process of flowing off your roof it can pick up some.

For which reason I use a simple countertop charcoal filter for it. Works fine.

Charcoal does not kill pathogens, it only adsorbs organics. Since the charcoal builds up organics in its pores, bacteria will also feed on the organics and form large colonies that could give you stomach problems. Make sure it is silver impregnated carbon which supresses the build up of bacteria. Unless you invest in an R.O. system with small pump, the easiest way to kill pathogens is to boil your water that you want to use for drinking (a minimum of 72C with 15 seconds is enough to kill all the pathogens).

you cant "boil" water at 72degrees

you could heat it to 72 but thats well

before it boils

You can actually but you would need to be at an elevation of around 9000m. At the highest peak of everest for example the boiling point of water would be around 72C.

Sorry, in a pedantic mood this morning.

When I heat water or pasteurise milk to remove pathogens I always BOIL it at 72C using a vacuum pump to lower the pressure so that the water or milk reaches boiling point at 72C, it saves energy. At home you need to heat it to 72C for 15 seconds. Most electric hot pots have temperature displays so it is easy to heat the water up then put it in plastic containers once the water has cooled sufficiently so that the water can be used for drinking.