Home » Auto Tips » Can You Mix Tap Water With Engine Coolant? What You NEED To Know

Can You Mix Tap Water With Engine Coolant? What You NEED To Know


The short answer is no, you can’t mix tap water with engine coolant. Distilled water can work, but it is not ideal. Soft water is the best solution. We’ll get into more detail below. 

We all know the oil in our cars has to be changed, but it’s less common knowledge that the engine coolant needs to be replaced as well.

Eventually, the chemicals that flow from our radiator and into our engine block to prevent overheating do break down and become less and less effective.

How frequently the coolant needs to be replaced is going to vary from vehicle to vehicle. The standard is about every 30,000 miles or every few years.

So what is engine coolant exactly? Engine coolant is the liquid that surges through your engine and keeps your car from overheating.

This is a tall order considering the controlled engine explosions that move your car forward get up to around 495 degrees F. These can lead overall engine temperatures up into the 200-220 degree Fahrenheit range when you are driving continuously.

To do its job properly, the fluid that gets pumped through your engine and prevents catastrophic heat damage MUST have a very low freezing point and a very high boiling point. Water alone does not meet these requirements.

To meet these specifications, we use a solution typically referred to as engine coolant. It is common for an additive called antifreeze to be included as part of this solution.

Pure antifreeze actually freezes and boils more quickly than water, but when combined, it actually lowers the freezing point of the mixture and increases the boiling point. It also prevents corrosion in your engine. Coolant is generally a 1:1 ratio of antifreeze to water.

Why antifreeze though? Water freezes at 32 degrees and boils at 212 degrees. Because engine temperatures can sometimes drop below or exceed these ranges we must use additives to prevent the freezing and boiling of the fluids within the lines of your car’s radiator.

If that liquid were to freeze it would break your engine. If the fluid reaches a boiling point it will no longer be able to serve as a heat transfer between the hot metal in the engine block and the car will overheat.

Engine overheating causes warping of several important components of the engine like the aluminum cylinders, engine head gasket, and water pump.

When water is mixed with antifreeze (which is made of a chemical called ethylene glycol), the freezing point is bumped down to -35 degrees, and the boiling point raised to 223 degrees Fahrenheit.

This makes ethylene glycol the perfect additive to our cooling system!

So now we know that mixing antifreeze and water together make a suitable concoction for heat transfer within the car’s cooling system, but we need to be specific on exactly what water to mix in with the antifreeze.

Tap Water Should Not Be Mixed With Antifreeze When Replacing Your Engine Coolant

Please save yourself the trouble down the line. Do not use tap water when it comes to your vehicle. While some engine coolants are designed to be mixed with water before being poured into the cooling system in your vehicle, you cannot just use any water that you please.

Tap water is full of minerals that will eventually form deposits inside your radiator, plumbing and water pump. This is also referred to as hard water scale.

This is all types of tap water that we are talking about here, no matter where you live! Tap water has mineral deposits in it by nature. You can’t put these minerals in your cooling system without causing problems down the line.

When tap water is repeatedly used in your cooling system you will start to get a buildup of calcium and magnesium. This build-up is also referred to as hard water scale and you’ve likely seen it on your household appliances.

When your radiator gets mineral buildup or hard water scale it becomes less effective at cooling off those hot engine parts. And even just a little build-up is a huge problem. A 1/16 of an inch of hard water scale will make your cooling system 40% less effective.

That means your engine is apt to get 40% hotter than it should be and that can cascade into many other engine-related issues.

A less effective cooling system can lead to your engine overheating. When your engine overheats it can, and if untreated will cause damage to your engine. Some engine parts will warp with the heat they are not meant to withstand.

Common parts that break and require repairs after engine overheating include a cracked head gasket (average replacement cost $1500), warped cylinders (average replacement cost $500) and water pump replacement ($350- $700).

A policy from Protect My Car can shield you from these high repair costs. 

Needless to say it is much cheaper to be proactive and replace your coolant with the proper ingredients before negligence or laziness leaves you without the convenience of your vehicle because it is in the shop undergoing a costly repair.

Since you are reading this article it’s pretty likely you’re wanting to replace your coolant yourself. It will probably cost you around $30 to complete this project. With the average cost of coolant repair at the mechanic being around $130 you’ll be saving yourself $100 in labor costs from the mechanic. Go you!!

If you’re trying to learn more about the ins and outs of changing your engine coolant yourself, there’s more on that to come, so bear with me.

To reiterate. Tap water inside your engine block is bad! Do no not mix your antifreeze with tap water

Distilled Water Isn’t The Answer Either

There’s a lot of information on the internet that recommends using distilled water when it comes to the cooling unit in your vehicle. I’ve even seen a very famous mechanic on YouTube putting distilled water in his cooling system!

The thought process here is that distilled water has had the minerals stripped from it and will not leave build-up deposits in your hoses and radiator.

While this is good in theory what this does not take into account is the distillation process. Here’s why you should NOT use distilled water.

When distilling, the water is heated into a gaseous phase. When this water boils off and evaporates it leaves behind the calcium and magnesium that once lived between it’s molecules. This process is called mineral stripping.

While we do need water that has been removed of these minerals for the coolant system, the process of distillation actually will leave the water ionically imbalanced. Essentially the distilled water solution is unstable because it is missing an electron. Distilled water will damage the metals in your engine if used repeatedly.

The Science Behind Why This Works

As the water evaporates, the calcium and magnesium take with them electrons leaving the remaining solution yearning to rebalance itself and gain a full set of eight valence electrons.

When you put distilled water inside your engine block that water will do its best to strip electrons from the metals it comes in contact with.

Essentially the gist of this without all the subatomic jargon is that distilled water is still damaging to the components of your engine just in a different way than tap water.

So steer clear of distilled water as well as tap water despite what most people are posting online.

Use Softened Water For Best Results

Softened water is the anwer here – it makes a difference.

The process of water softening takes tap water and removes the minerals within it. The main minerals in tap water are calcium and magnesium and there are also trace amounts of iron depending on where you live.

So, softened water, like distilled water, is free of calcium and magnesium. However, the process of removal of these minerals is vastly different. And that makes all the difference. Here’s why.

The large distinction between these processes is as minerals are removed in the softening operation they are replaced with a sodium ion. The solution that results here is stable, it’s not trying to take electrons from substances it comes in contact with. This makes softened water safe to use, as it won’t destroy the internal systems of your vehicle.

Softened water, unlike distilled water, won’t strip the metals in your engine block of their electrons, which can cause damage to your engine. With the average engine repair cost sitting at around $3,500 dollars, it pays to be prudent. Be prudent and spend the extra time getting soft water next time you need to make a repair on your car.

Softened water is completely safe to put in your engine and won’t cause damage, unlike tap water or distilled water. So be smart. Stick to soft water!!

You Can Either Make Soft Water Yourself – Or Buy A Water Softener

So now that you’re aware of the fact that you need to have soft water to mix in with your antifreeze let’s talk about where you can get it.

  1. Your tap if you have a water softener. You can get one of these from Amazon/Home Depot/Walmart 
  2. You can make your own using the process detailed below
  3. Ask your family or friends who live nearby if they have a water softener system installed in their home. If they do and agree to give you some of their water, you can bring gallon jugs or another water transport container, fill them up from the tap at their home. I would verify that the water is actually softened.

Unfortunately from my research I haven’t been able to find soft water bottled that you can purchase online. What I did find was distilled water claiming to be soft being retailed. Please don’t buy distilled water pretending to be soft water. There is a difference, don’t let the water companies fool you by claiming they have soft distilled water.

LUCKILY you can make softened water pretty easily at home. Here’s how.

How to make your own softened water without installing a water softener in your home

  1. Bring your water to a boil.
  2. Next allow the water to cool. If your water is temporarily hard meaning it contains bicarbonate and calcium ions then you are good to go and the boiling process will fix this problem. For most of you the water is permanently hard, in other words it contains calcium and magnesium sulfates. If your water is permanently hard, proceed to step two once the boiled water has cooled.
  3. Add washing soda to your water. Washing soda, which is similar to baking soda can be found and purchased at most large retailers like Walmart or Target in the laundry section. For exact mixing proportions check the packaging of the washing soda.

Coolant or Antifreeze? Which Should I Combine With My Soft Water?

Antifreeze and engine coolant are used interchangeably, however they are not exactly the same thing. Let’s clear up this confusion.

Engine coolant refers to the liquid mixed solution that surges through the engine block in your car keeping it from overheating. Essentially exactly as its name describes. It is important to note that it is a solution, meaning it is made up of a mix of several substances.

Antifreeze is a chemical, ethylene glycol, which is found in most premixed engine coolants that are ready to be added to your vehicle.

It is also sold separately as a pure substance ready to be mixed with SOFTENED WATER and then funneled into your car’s cooling system (after you have read the manufacturer’s instructions and safety warnings).

To reiterate, your options here are to purchase a premixed engine coolant that is ready to be added to your empty, clean, engine coolant compartment in your car. Or you can purchase anti-freeze and mix a 1:1 ratio with softened water. Always read the mixing instructions to verify safety procedures and mixing ratios which may vary from brand to brand.

I have included some information further along in this article to help you clean out your engine coolant system of all old, used and dirty coolant and to help you dispose of it properly.

REMEMBER antifreeze is toxic and has to be disposed of properly! Please be sure to keep your used and replacement coolant away from animals it tastes sweet to them and they will drink it.

You Don’t Have To Mix All Coolants With Water

Now that we understand the fundamental differences between engine coolant and antifreeze this question is much more manageable.

Some engine coolant will come premixed from the store and is ready to be added to your vehicle as is. It does not need to be added to water. If you are not sure if you have purchased a premixed engine coolant, check the instructions on the label.

To determine what type of engine coolant your car requires refer to your car’s owner manual. Generally your car will be labeled near the fill spot as well showing what color of engine coolant is recommended. They are traditionally green or orange.

Antifreeze is a pure substance that does need to be mixed with equal parts water to make an acceptable engine coolant. What type of water everyone?? SOFT WATER.

Please check the manufacturer’s instructions when mixing antifreeze before adding the fluid to your vehicle. Be sure to follow all safety precautions detailed by the manufacturer as well. Remember that this stuff is toxic and can kill mammals that drink it.

Why Do We Add Antifreeze To The Water We Use To Cool Our Engine?

  1. Water is corrosive and will eventually corrode the engine and cause rusting of the internal components it comes in contact with making them unable to do their job.
  2. Water has a relatively low freezing point, but in most areas of the world winter does get cold enough to bring fresh water to a solid ice. If this was to happen within a vehicle it would break the engine.
  3. Coolant also keeps the water from boiling when it gets too hot. When engine coolant boils, or any other liquid for that matter it cannot get any hotter while in the liquid form. What this means is that it is no longer effective at receiving heat from your engine or cooling anything down.
  4. Essentially coolant protects your car’s cooling system when driving in extreme weather climates. So if you’re planning on adventuring towards the poles in your vehicle or driving through death valley you should make sure your cars coolant levels are full and have been mixed with the appropriate coolant for your vehicle

What Happens When You Add Water To Antifreeze?

The properties of water shift when forming a solution with antifreeze. The temperature at which it boils increases. This makes it better at withstanding heat and in turn improves its ability to cool down what it comes in contact with.

Water is an excellent conductor meaning it receives energy, or heat, well. When you add antifreeze to the mix it becomes even better at conducting by nature of the boiling point increasing.

Essentially the fluid solution can retain more heat before being converted into a gaseous state. Layman’s terms here is that the solution containing antifreeze is better at cooling down the hot engine parts when it runs through your engine blocks.

Antifreeze is also a carrier for several additives that reduce the solutions corrosive effects. These additives may include but are not limited to sodium silicate (an aluminum anticorrosive) and antifoaming agents.

You want to always read the manufacturer’s instructions to see how and if you should mix coolant with water.

It’s also important to note that antifreeze is very dangerous to animals. It is enticing to dogs and cats because it tastes sweet to them. They will try to drink it if given the chance and it is usually deadly.

Make Sure You Dispose Of Your Antifreeze Properly

Be careful with your used engine fluid during the removal process as it is toxic and should not simply be dumped out with the trash or down a drain.

It needs to be disposed of properly. Be sure to transfer the liquid into something watertight. It needs to be in a container that will be feasible to put in your car to take in for recycling.

Used engine coolant can be properly disposed of pretty easily. Most mechanics will take it off your hands for free (they make money when they sell it off to the disposal companies).

You can also recycle the fluid at your local disposal center or hire a private waste disposal company to come pick it up from you.

I reiterate here, engine coolant is toxic. We do not want it in our water systems, in our pets or in our children. That would be bad. Be responsible.

What Type of Engine Coolant Should I Use?

Wouldn’t it be lovely if most car manufacturers used a consistent type of engine coolant? Well they don’t and I recommend checking your car’s user manual to find the manufacturer’s recommended type of engine coolant. From there you can choose a brand or generic amongst this category of coolant.

There are three common varieties of engine coolant: they are inorganic additive technology, organic acid technology and finally hybrid organic acid technology.


This solution a bit outdated and is less superior than its competitors nowadays. As there are now more effective options on the engine coolant market you typically only see inorganic additive technology in older vehicles.

If your car uses this type of engine coolant it is important that you stay on top of flushing your system and replacing your coolant.

Inorganic additive technology coolant must be changed every 24,000 miles or two years, whichever comes first. This is far more frequent than newer coolants that are on the market.


The next coolant we are going to discuss is much more with the times and requires far less maintenance and upkeep. It is increasingly popular in vehicles newer than the year 2000.

Organic acid technology coolant, which is widely used by General Motors, only needs to be changed every five years or 150,000 miles! That is a remarkably long length of time that you can go without replacing your coolant. This saves these car owners time and money involved with maintenance procedures.

This variety of OAT coolant is traditionally orange yellow in color, but not always. 

It is derived using fully neutralized organic acids and azoles and these are the components that make the fluid anti corrosive. This is also where the substance received its name.


Finally we have Hybrid Organic Acid Technology which is a slight variation of Organic Acid Technology. Both of these coolants have essentially comparable replacement cycles

Change The Fluids In Your Cooling System Every 30,000 Miles

Eventually the chemicals in antifreeze do breakdown and become less effective at keeping your car’s temperatures moderate. When this happens your car is at greater risk of engine overheating which can lead to costly repairs.

Its best to be proactive here and change this antifreeze combination every 30,000 miles or so for most vehicles. Your car’s user manual should make a recommendation on this mileage specific to your vehicle in the same section where they detail what

What The Color Of Your Anti-Freeze Means

Until very recently the most commonly used color of antifreeze was a neon green. This is because this is the color that is associated with the variety of coolant called Inorganic Additive Technology or IAT.

IAT has been on the decline as the choice of car manufacturers simply because there are now more effective coolants on the market. Increasing in popularity are orange and red coolants which are typically of the Organic Acid Technology variety of coolant.

While these types of coolants are traditionally these colors you should always verify that you are using the proper coolant for your car using your owners manual of your vehicle.

Nowadays coolant color doesn’t mean as much as it used to. The purpose of companies who manufacture engine coolant dying their products is for marketing purposes as well as safety concerns.

Antifreeze is by nature clear. By making it a ghastly bright color it does a couple things. It makes the substance easy to identify when compared to water.

This is super important because remember antifreeze is very toxic. If you, your family members or friends or your animals were to drink it it can be deadly. Contact a poison center or go to the emergency room if you think you’ve accidentally consumed this stuff.

Antifreeze companies can add whatever color dye they would like to their product. For this reason I encourage my readers not to use color alone as a way to distinguish the variety of antifreeze that is good for your car.

Can you use battery water as a coolant or other substitutes?

It depends on what you consider to be “battery water”.

Some individuals refer to battery water when talking about the liquid within car batteries called electrolyte. Electrolyte is a mixture of sulfuric acid and pure water. It should never be added to the coolant system in your car. Please do not drain your battery into your cooling system.

To others the term battery water refers to the water that you add to your battery. This water is just distilled water.

Putting distilled water in your radiator is a generally accepted practice however I encourage people to opt for soft water over distilled water. My reasoning here is that soft water has a full set of valence electrons whereas distilled water does not.

Essentially that means that soft water will not strip the metal in your engine block in the same way that distilled water will. If you are confused by this I cover more on the science behind distilled water and soft water towards the beginning of this article.

Opt for soft water over distilled water. Whatever you do though, don’t drain battery fluid into your car. I’m willing to bet it will go poorly for you and your car.

How to safely and effectively drain and flush your cooling system

Most of my readers are interested in engine coolant because they are actively undertaking the replacement of their engine coolant themselves. This is awesome and will save you guys some money, however, you need to make sure you are replacing the fluid properly and especially that you dispose of your old coolant in a responsible fashion.

  1. SAFETY. Cooling systems are pressurized and you need to ensure you are using your car when the engine is cool. We don’t want you to get scalded by super hot engine coolant, okay? Please pay attention to these warnings he gives you.
  2. What preparations you need to make before flushing your engine’s cooling system. Generally, it is suggested that you use a chemical coolant flush several days before actually flushing your engine.
  3. The section in which you can look within your owner’s manual for information regarding what engine coolant you should personally use for your car.
  4. How to disconnect and reconnect the hoses in your car’s cooling system so that you can attach a hose and flush the system.
  5. How to ensure the engine cooling system has been drained entirely.
  6. What to drain your old cooling fluid into.
  7. Safe handling and disposal of used engine coolant.
  8. He even shows you the change in color with each of his five or so engine flushes!
  9. Finally, the video shows him replacing the engine coolant with a new coolant.

Coolant Leaks Can Be An Expensive Issue – Get A Vehicle Service Contract & Protect Yourself From Repair Bills

Car repairs can be absurdly expensive, and you can expect those unexpected repairs before too long no matter what vehicle you drive. 

If there’s an issue with your engine coolant, it could cause major damage to your engine. For most vehicles, a new engine can cost up to $5,000.

If that seems absurd to you, luckily you aren’t alone.

A vehicle service contract from Protect My Car can help cover the cost of these excessive repairs. In fact, you could pay as little as $100 dollars for that $5,000 engine replacement.

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When you walk into the repair shop with a coverage plan from PMC, you can rest assured that you will never pay for these repairs listed here. You pay a $100 deductible, just like insurance and we pay the rest.

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About Protect My Car

Protect My Car is an extended auto warranty company. Our goal here at Protect My Car is to eliminate your worry of being financially responsible for an expensive mechanical breakdown. With our extended auto warranty, you don’t have to worry about being fully burdened with the cost of a covered repair.

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