If the battery has easily detachable caps then a top-up with distilled water may be required from time to time. Prolonged overcharging or charging at excessively high voltage causes some of the water in the electrolyte to be broken up into hydrogen and oxygen gases, which escape from the cells. If the electrolyte liquid level drops too low, the plates are exposed to air, lose capacity, and are damaged. The sulphuric acid in the battery normally does not require replacement since it is not consumed even on overcharging. Impurities or additives in the water will reduce the life and performance of the battery. Manufacturers usually recommend use of demineralized or distilled water since even potable tap water can contain high levels of minerals.

Well... I never tried to take the water out from the battery and test it, my bad 

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Added on September 28, 2010, 12:40 pm

Well... I don't really trust Wiki but still here's a quote from there:
"Non-laboratory uses
Distilled or deionized water are commonly used to top up lead acid batteries used in cars and trucks. The presence of foreign ions commonly found in tap water will cause a drastic reduction in an automobile's battery lifespan.
Distilled or deionized water is preferable to tap water for use in automotive cooling systems.[6] The minerals and ions typically found in tap water can be corrosive to internal engine components, and can cause a more rapid depletion of the anti-corrosion additives found in most antifreeze formulations.[7][8] Distilled or deionized water is especially important in automotive hybrid system component cooling systems, mixed with hybrid system coolant, to prevent corrosion and/or electrolysis of hybrid components.[9]"

That settles one question.... 

I'm living proof... drank distilled water and deionized water everyday 

When famine breakout, and no potable water, evaporated and condensed distilled water is the only water that is safe to drink and easiest to obtain.

The problem that excessive distilled water cause it since there are no minerals within it, it tends to absorb minerals from body which leads to demineralization of body

I am from Engineering background.. not medical.. to me, the flow of substance is absorb

it is like people argue about the terms for place to urinate... toilet? washing closet? lavatory? aint it the same? but use differently in different place

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Added on September 28, 2010, 4:06 pm

Yes... I am talking about possibility of drinking distilled water as in general.

and yes too to your assumptions that people do not have the time and energy to do distillation several times...

100% maybe required for medical purposes... but for survival purposes? not quite... and what does 95% pure and 99% pure have to do with keeping me hydrated....

Pipe water, rain water, distilled water, deionized water. All drinkable. All are hypotonic. Drinking hypotonic liquids does not cause your cells to burst.

Nobody pees pure distilled water, so minerals are leaving your body all the time. If you switch from drinking pipe water to distilled water, you're reducing your mineral intake, but only very slightly. No pipe water contains even remotely the same concentration of minerals as urine.

You get minerals from your food too. In fact, practically all your mineral intake comes in your food.
http://www.who.int/water_sanitation_health...s/en/index.html

What makes pure water hypotonic? are you saying that water distillers kill people?