Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Reverse Osmosis water in battery

Is it OK to add reverse osmosis water instead of distilled?

I believe RO leaves behind slight amounts of minerals, but distilled might leave behind a few chemicals too, like chlorine.

So is it 6/half a dozen? Or is distilled the only way to go?

Also, is it possible to revive a dead battery by topping it off with water and slowly charging it with a charger?


Distilled water is the way to go. After all, it isn’t that expensive.

If the battery is truly dead, and water isn’t the issue, adding more water won’t save it.

Distilled is the right water for a battery.
“dead” means different things. If a battery is discharged say by leaving the lights on all night, it is called by most folks “dead”, but it will usually take a charge and soon be good again. If the fluid in the battery is low, which happens over time, the battery will not hold a charge as well as it should, nor deliver the current you need. In that case, topping up the fluid with distilled water to the line will be good for your battery, you should check the level every 6 months or so to insure long battery life. If the cells have flake from the plates accumulated in the bottom, they will short out and the battery is effectively at the end of its first life. A battery shop can remove the plates, clean the cells and restore the battery for a few more years of life, this is a sort of battery ressurection. If the specific gravity of the fluid, the acidity is too delute, the fluid can be changed out to bring the battery back as well. so you see the term dead battery covers a lot of ground.

Thanks i9, very helpful. I believe the latter is the issue. If the charge doesn’t take I’m just going get a new battery. Although… how safe is it to change the fluid out for a do-it-yourselfer? And what is the cost of the fluid?

Don’t change out the fluid (a sulfuric acid solution). If the battery won’t take a charge, get a new one.


The water may not matter much. If your battery is not old and I don’t know enough to say what is old for various lead acid battery types, your battery may be sulfated. Google “Sulfated battery” and do some reading. I have a problem battery too and don’t know enough at this point to advise a way to overcome sulfation.

Here is some reading for you.

Reverse osmosis water is fine. Well water with lots of lime in it is not.

If the dead battery is still good, it will be revived. If it won’t take a charge, you will know what the next step is. The battery does the decision making in any case.

The distilled won’t break the budget, so why use anything else?

RO water is fine…Automotive batteries don’t last long enough or use enough water to make any difference…

Few “dead batteries” will revive…You can TRY to charge them, try 5 amps for 10 hours…Then perform a load test. If the voltage drops below ten and does not instantly recover to above 12, the battery is junk…

you can use clean rainwater too-Kevin

You can also use clean rainwater-kevin(got a double post sorry)

RO water is just highly filtered water. It’s about 98% pure water. Distilled water is 99% pure water. Distilled water is created by actually boiling water…then funneling the steam through pipes into another container where there’s nothing left but pure water. All the other contaminates were left behind because they were too heavy.

do not attempt to change the fluid in your battery at home. This is for a used re-built battery shop to do, just like cleaning out the cells etc. I would not use rain water either, these days you dont know what might be in it. The air is full of stuff, and anyway raindrops form around dust motes. But if you want to know what the specific gravity of the sulfuric acid/water mix in your battery is, you can buy a tester for very cheep at any parts store, and that will give you a clue about the condition of your battery.

“I would not use rain water either, these days you don’t know what might be in it”

-Yeah, it would suck to get acid rain in your battery. LOL

OP, you never, ever add anything other than distilled water to a battery that has already had electrolyte in it.
By dumping what’s in there and refilling with fresh electrolyte you will be upsetting the acid/water ratio in the battery when the charging process starts.

No, reverse osmosis can not/does not remove all the dissolved chemicals. Distilled water always removes all dissolved chemicals. “Catch” rain water can be used since it has been distilled (evaporated) naturally by the sun.

Go buy yourself a gallon of distilled water at the supermarket for $1.50. That’s a heck of a lot cheaper than getting stuck on the road and then having to buy a new $80 battery. (Plus any towing cost, then mechanics charges.)

The moral of this is: Don’t screw around with strange sources of water for refilling your battery. If you are on a boat then get a rainwater catch device if you can’t buy distilled water. All bottled “drinking” water, like Perrier, natural spring water etc., etc., have dissolved chemicals that will destroy your wet lead-acid batteries.


distilled water only in batteries. I’m not a real smart guy, but when you know a few men who own battery shops and they tell you distilled only, well that’s what you do. They all reasoned it the same. Using distilled water does not wash the deposits off the plates so they collect at the bottom and short out a cell turning a 12.6 volt battery into a 10.5 volt battery.

I have tried adding more water and acid as needed to batteries, but have found in my experience once you need to do any of these you might as well replace the battery and save doubts and failures.

So much bad information on this thread. RO, or more specifically RODI water would be fine. Chances are it would be more pure that the distilled water you purchase at the store. Yes, in theory, distilled water is 100% pure, but it will still pick up trace minerals and metals depending on the equipment used in the process of making it. Don’t believe me? Get yourself a TDS tester (actually just a conductivity meter) and test your trusty “distilled” water. Process’s that require the purest of pure water (such as CPU processor fabs) all use RODI water.

Now, the OP did not specifically state RODI, but rather RO water, and yes I would stress that the RO water must also past through a de-ionization filter, in which case you will be fine.

Reverse osmosis (RO) is a water purification technology that uses a semipermeable membrane to remove larger particles from drinking water. It’s a filter system, usually purchased to make drinking water more palatable and to prevent the clogging of shower heads and such where the water is full of minerals. Note that this water may be perfectly safe to drink, but clogs the shower head.

Distilled water has had all mineral contaminates left behind when the water was turned to steam. It was then condensed back into water. All the minerals have been removed.

It’s the minerals that generally what create havoc with cooling systems. They build up in and clogs the tubes in the radiator. They can build up on the thermostat too and interfere with its operation.

I would put only distilled water in a battery.
Your car, your choice.

I should point out that Volvo has made a good point, this is a very old thread and I’m sure the OP is long gone. There’s just so much misinformation in it that I felt compelled to post.

I agree with comments here that using distilled water in a battery is the right thing to do – given the likely nature of available alternatives.

What I mean is that all water purification methods have their pluses and minuses, this includes distilled water. As a simple example, double distilled water exists (although not sold in most places), which should be enough to convince most people that there are contaminants remaining after a single distillation process (even though those are not significant for car battery use).

The OP probably had some kind of RO system at home or otherwise had access to RO water. The usability of that water in a battery DEPENDS ON the details of the RO system. Generally, an RO system removes contaminants based on size (while distillation removes based on boiling point), including very, very small molecules and ions. And an RO system can have (but doesn’t have to have) additional components, such as to remove based on charge (de-ionization) and based on additional filtration.

Because of the dependency on exactly what the RO system might be, the simplest, and safest, way for most people is to ‘just use’ distilled water from a store or other known source.