Be forewarned that this one is a head scratcher, not a definitive answer (yet).

At 07:58 PM 2/16/03 -0500, Richmond (from Connecticut) wrote:
>"on your battery testing and maintenance page you give some wrong advice you should never add plain water to a battery only distilled water as plain water can ruin a battery because of the minerals in it. You should rewrite your page to include this info. I know many people who have ruined a battery by adding plain tap water to it"

Some of these general purpose articles are the toughest to write, because the easy and most obvious answer is not necessarily cast in stone. I will tell you right out that if you want to always put distilled water in your car battery, that would be perfectly okay, and you may rest assured that you will not be harming your battery by doing so. And if you absolutely believe that distilled water is the only thing to use, or that such minor inconvenience is easier than taking the time to collect and understand all of the facts, then you need read no farther. Have a nice day. Bottom of page please. Or if you have a few more minutes to read on, you might just decide that you may not need the inconvenience of distilled water.

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Oh, still here? My reference to "plain water" on the previous page was originally meant as an admonition to add only water and not battery acid when topping up your battery. The respondent quoted above apparently took "plain water" to mean "any kind of water", and also apparently wanted to emphatically express his understanding that distilled water is the only thing acceptable to use in a battery, and advising people otherwise is some serious moral infraction. Against my better judgment I did respond to his message, and that lead to (at last count) five more follow up messages in which he pretty much took exception to any logic I set forth.

During this discussion I never actually claimed that some other type of water would not hurt your battery (although I was playing devil's advocate to make a point). I was just diligently asking him to explain why he though it would harm a battery, and to present some evidence to support his claim, and hopefully to shed some light on why something like "drinking quality water" might actually harm a battery. I won't reproduce the entire discussion here, as it was many pages long, but the end result was that he finally went away dejected (my impression) when some simple logic continued to prevent him from absolutely proving his claim (or he likely thought I was just being bullheaded and didn't want to waste any more time).

The problem with this discussion is that you have to be careful with your logic. If you put tap water in your battery, and then your battery dies, that does not necessarily mean that the tap water had anything at all to do with it. At least this does not follow logically, as it is only inferred by casual association until you can show for certain exactly why the battery failed. Batteries fail for lots of different reasons, and they all will fail eventually, even when using distilled water. So be assured that if you add tap water to your battery it will eventually fail. But I stand here with an open page available asking anyone to show conclusively that the tap water had something "significant" to do with the failure.

During that vigorous interchange of ideas both he and I were browsing the web for information. I'm sure he was trying to prove his claim, and I'm also sure he thought I was trying to prove the opposite. But in fact I wasn't trying to prove anything except that he couldn't logically draw the conclusion he was after. But I was diligently searching for the truth. And the truth is, so far I have found nothing to conclusively prove that "drinking quality water" will ever harm your car battery. This gets a lot longer, and you can bail out any time you like. Bottom of page please.

Not being one to rest on a half truth or a large knowledge void, I proceeded to recruit some assistance (on the sly). I posted a "challenge" to the mgs e-mail list in the following form:

>I have a feeling this is going to start an avalanche of vaguely related response, and maybe even a religious war or two, but that is not my intention. I have only one very specific question.
>
>When discussing what type of water to use for topping off a car battery, the common response is usually "distilled water", and this is sometimes (fairly often) followed by "anything else will ruin the battery". The simple form of my question is, "Why?". Now before you jump into this with both feet, please stick to the facts and try to suppress traditional rumor and personal opinion (however difficult that may be), and also consider the following.
>
>I have done some web searching and read what is offered by several of the major battery manufacturers. Some say to use distilled water, with no further explanation. Some say to use "good quality drinking water" with no mention of distilled water, and no other explanation. At least one says to use distilled water, followed by "If you don't have distilled water use drinking water as better than nothing", (but of course distilled water is also better than nothing). In most cases there is little or no distinction made between distilled water or drinking water.
>
>The curious part is that in no case did I find any battery manufacture making any statement to the effect that any type of water (at least "drinking quality" water) would actually harm a battery. This strikes me as being quite "significant" in light of the fact that they have to cover warranty returns. It seems to me that if there was any significant chance that "drinking water" would harm a battery, the battery manufacturers would be all over this fact and might even go so far as to void the battery warranty if you use anything other than distilled water. But as much as I search I have found no such statement from any battery manufacturer. [See update 17 May 2003 below]
>
>So here's the challenge, and please stick to the facts, not speculation. Can anyone come up with documented proof that drinking water might actually harm a car battery, and if so, what exactly would be the mode of failure of the battery as caused by the water? Best submission with factual proof will get a full page write-up with credit and name attached in the tech section of my web site (and maybe some print publications as well), and maybe some additional prize for furthering the education of mankind (but probably not the Nobel Peace Prize).
>
>I need real cause and effect here. A casual relationship is insufficient. "My battery died after adding tap water" doesn't cut it. Lots of batteries die (like all of them eventually) for various reasons. We have to know why it died, which could require an autopsy with photos and chemistry test results. Otherwise I would like to see some results of controlled parallel lab tests on batteries using distilled water and "other" water. I am looking specifically for any DOCUMENTED reason why "drinking water" would actually harm a car battery.

I am sorry to say that the many hundreds of people on the mgs e-mail list only generated a total of seven open responses (and 4 more off list) before the subject "detoured" off on a different thread. Although a couple of the respondents did a decent job of explaining how a battery works, and a few things that "might" cause it to fail, I believe the original challenge remains (for the most part) unresolved. My casual inference here will be (until shown otherwise) that "drinking quality water" will not cause any significant harm to your car battery. Anyone reading this is free (even encouraged) to contribute some logical proof to the contrary, but please avoid speculation and provide some supporting evidence that will stand the test of logic (that what you say can actually be shown to be true).

To get you started on the right foot, here are some web references for such information. Keep in mind that deep cycle batteries are much different than car batteries. In operation deep cycle batteries regularly process relatively large amounts of water, as much as a gallon per cell per year in some cases. Car batteries are generally kept near full charge, and their water usage may be measured in ounces per year. Please let us stick to discussion of car batteries.

From the world's largest maker of car batteries, Exide:
www.exideworld.com/faq/faq_auto.html#maintain (link broken 7/22/12)

Interstate batteries website, in their section on watering batteries
www.ibsa.com/www_2001/content/faqs/tech_talk/maintenance/faq_tech_maint.htm (link broken 7/22/12)
Click on "Watering Batteries"

Johnson Controls website, from their battery maintenance section
http://www.jci.com/bg/BatteryBasics/bb_storage_tips.htm

Car & Deep Cycle Batteries, Frequently Asked Questions:
http://uuhome.de/william.darden (link broken 7/22/12)

Over 150 of the largest battery makers and many hundreds of brands:
http://uuhome.de/william.darden/batbrand.htm (link broken 7/22/12)

Independent Battery Manufacturers Association, list of manufacturers:
www.thebatteryman.com/battery_manufacturers.html

Well that should be enough to keep you browsing until you get bored.

Best regards,
Barney Gaylord

Update 06 MAR 2003

In summary, the original responses were:

>" I wouldn't be surprised if certain particular mineral-and-pH combinations turned out to be harmful to car batteries, ...."

>"I've been using tap water in batteries for 40 years and haven't killed one yet."

>"Technically speaking, "drinking water" will not harm the car battery."

>"We (my father & I) have used tap water in car batteries for as long as I can remember with no apparent ill effect."

>".... I have not seen any tests done to prove this out but this is why distilled water is being recommended."

>"I'd imagine that the minerals in the tap water may have some detrimental effect on the chemistry. On the other hand, I've used tap water for many, many years in cars and the batteries have almost always lasted past 5 years."

>"Jim Albeck of Agoura Hills, Ca. .... has a neat item that has saved many a battery and more important, a whole lot of money"

>"Drinking water' in the UK at least, can legally contain a whole range of other compounds .... and pure spring water has been known to fail drinking-water purity tests because it did NOT contain things like aluminum sulfate and chlorine added by state-run water purification plants."

>"If .... water from the tap or typical mineral water as the commonly used drinking bottles contain ...., the liquid mixture between the sandwiched plates get contaminated with wrong materials."

>".... The water is evaporating, but the mineral content it carried is left behind. Over time, the concentration of minerals will build up to a much higher level than that of the water you're using."

Credit to Craig White for the most effort at finding some research reports on the web. Once you weed out the problems specific to deep cycle batteries, the many remaining seem to hint or imply and even state openly the one should not use tap water in a car battery. But none of them ever actually commit to a proof that the stuff will harm a battery, or place any quantitative values on how much harm it might cause. One of the most comprehensive reports on an attempt at accelerated life testing states outright that it is inconclusive and the test does not accurately reflect real world usage. Bummer.

I have more recently received responses loosely defining a couple specific types of water (heavily mineral laden in different forms) that could possibly harm your battery, and a reasonable explanation of why an how. But still no conclusive proof that this would actually happen, or how much water is required, or how long it might take to happen (like less time than the normal life span of the battery). Additionally, the types of water being described might possibly be "tap water" in some areas, but might be highly suspect to be called "drinking quality".

Surely there will be more to this later.

Update 17 MAY 2003

At 07:49 AM 5/17/03 -0400, Brian (bdmxyz@austarnet.com.au) wrote :
>from http://www.supercharge.com.au/aboutmainframe.htm (link broken 7/22/12)
>"This guarantee however is void if the battery has been subjected to overcharging, abuse, faulty vehicle charging system, neglect, failure to maintain acid levels, additives other than distilled water, tampering of markings or broken or removed vent plugs, capacity that is not recommended by original equipment specification."

Thanks for the note, Brian This is (surprisingly) the first noted instance of such a warranty disclaimer (maybe not to be the last).

This still does not say that using any other type of water will actually harm the battery, only that it will void their warranty. It is in fact the easiest way to avoid needing to define what type(s) of water may or may not harm a battery, or to what extent. By simply saying "distilled water only" they can avoid the issue entirely and not even have to engage in the discussion.

This may however also reduce sales of their product, which may be the reason we don't see this disclaimer more often. Other battery manufacturers may feel that the problem is not significant enough to risk "discouraging" the customers with such a statement. Some other manufacturers openly state that "drinking quality water" is perfectly acceptable for use in their batteries. Either they think it will cause no harm, or perhaps honoring a few more warranty claims is good economics compared to reducing sales. I could easily believe this last concept, as I am forever pessimistic when any vested interest is involved.

Barney

Addendum, 5/5/2007:
Here's an interesting comment from the website of ROLLS, North Americas Best Deep Cycle Battery (www.rollsbattery.com).

"Check the height of the electrolyte twice a month."
Note they are talking about deep cycle batteries that process lots of power in and out daily, and so may use a substantial amount of water. Car batteries do not need to be checked this often, once every two or three months is usually adequate (six months if the car is not used much).

"If necessary replace with approved water only. Many times domestic water is satisfactory. Water with a high mineral content is not satisfactory. Do not use water that is difficult to create a lather when washing your hands with soap and water."

Now there's the sort of test anyone can do at home. If your soap lathers easily the water should be good for use in a battery. That bit is right from the mouth of one of the world's largest battery makers.