How to Make Tap Water Safe for Saltwater Aquarium?

How to Make Tap Water Safe for Saltwater Aquarium?

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Seeing as how water is the main component of keeping a saltwater aquarium, having good quality water on hand will be essential. You want to ensure it will be safe and clean for your aquarium. The obvious and most readily available source of water is what comes out of the sink. But, just because it’s water, doesn’t mean it’s going to be suitable.

So, how do you make tap water safe for a saltwater aquarium? There are many options and, of course, your budget will play a huge factor. You can use tap water, bottled water, distilled water or filtered/purified water. But none of these are going to provide the certainty in the same way that Reverse Osmosis (RO) will.

Should I use straight tap water from the faucet?

No, you shouldn’t use straight tap water for your marine tank. There are a host of issues that arise if you use it right from your faucet. There are many impurities that fill municipal water supplies, none of which will be good for your saltwater aquarium. The treatments cities put into their water are things like chlorine, fluoride, chloramines, among many others

Problems with Tap Water in a Saltwater Aquarium

All of this is going to be horrible for your aquatic life and you have no control over what goes into your tap water. You don’t know what gets added, when it gets added or in what concentrations. Also, when repairs and maintenance occur, things like sediment, increased heavy metals or other toxic components can make spikes in your water readings.

In using it, you run the risk of hurting your fish, developing algae blooms and accumulating heavy metals in large quantities. There could also be a buildup of other things like pharmaceutical drugs and bacterial substances that will be the ultimate demise for your aquatic life.

Tap Water Chemical Composition

There are around 20-30 contaminants laced in most sources of tap water. The following is s a small list of some of the more common ones found in many municipal water systems:

  • Ammonia: poisonous to aquatic life
  • Chloramine: reduces the oxygen capacity in fish blood
  • Fluoride: poisonous to aquatic life
  • Nitrates: foster algae growth
  • Phosphates: foster algae growth
  • Silicates: encourage diatom blooms

Although phosphates, nitrates and silicates are part-and-parcel to water’s composition, tap water tends to have high concentrations of these. If they go into the tank’s environment, problems that already reside with these in the tank will become worse. These things will, more than likely, end up killing your fish.

Only Use Tap Water in a Dire Emergency

That said, if you’re in an emergency situation and you only have to use a little, it should be fine to add. But in no way does mentioning this condone the regular use of tap water. 

In the case the emergency has to do with the water’s chemistry, avoid using tap water. If you can at least filter the water, you’ll be better off than using it straight. But even filtered water is iffy at best.

Will filtered/purified tap water be okay to use in my saltwater aquarium?

Home filters are great for drinking and cooking water, but not so much for your saltwater aquarium. Obviously, you can use it in a pinch. But it shouldn’t be your go-to solution for filling your tank, for regular water changes or dealing with chemistry issues.

The filter’s design for a tap adapter or a water pitcher helps remove some of the things plaguing municipal water. But, they don’t filter out everything and you’ll go through these filters rather quickly, especially if you’re using a pitcher. So, this may end up costing you more money than you bargained for in the long run.

How about distilled water? Is it pure enough to use in a saltwater aquarium?

As much as it may seem like a good idea to use distilled water, it’s not. It does provide very clean water, but, for a saltwater tank, the process removes too much of the good stuff. 

Plus, not every producer of distilled water uses the same process, so you don’t know what kind of chemicals went into making it. It should be evaporated water, but not every company is honest and forthcoming.

This means it still needs to go through filtration so it’s clear of all pollutants. But, like tap water and filtered water, you can use it in small amounts for topping off the tank.

Will bottled water work for a saltwater aquarium?

For a stable and reliable source of emergency water, bottled water is the way to go. It’s easily storable and obtainable, so it’s a popular choice for many aquarists. If you buy prepackaged store bought bottles, contact the company before hand to see what their filtration process is.

Local Water Stores

Going to a water store in your area will offer water they manually maintain. This means you’ll get high quality water that’s free of dissolved solids. Many use a high-output RO system, the same kind most aquarists use but this is on a much larger scale. They’re often very helpfull too.

Grocery Store Refills

You could also go to the refill station at the grocery store. But these aren’t monitored nearly as close as at the water store. Plus, it may or may not be RO water and the filter may not have changed in quite some time. So, if you go with this option, you should bring a quality TDS meter (see Amazon) with you.

How to make tap water safe for a saltwater aquarium?

You have some options to choose from when wanting to make tap water safe for your aquarium  You can get a dechlorination product, use an aquarium conditioner or you can get an RO filtering device.

Testing Tap Water

But, before determining the best method for your aquarium, you’ll have to get the water tested. There are a couple of ways you can do this: you can get your own testing kit or send it to a professional lab. The results will provide guidance on how you should go about making your water safe.

Even if you get a desirable result, there are a host of things that can happen to your local water supply. You cannot afford to make any mistakes when it comes to your tank. But it will depend upon where you live.

This is why some people use tap water and never experience a problem. Yet others use a little bit for an emergency and end up having serious algae blooms.

Dechlorination Products

There are a few dechlorination products to remove chlorine, but it may not be enough to rid the water of everything in it. These only remove chlorine and some manufacturers will add a feature to remove chloramine. But, that’s it. If your test results show there’s more than chlorine present, you’ll have to use something else.

Aquarium Water Conditioners

An aquarium water conditioner is another viable option. These are more all-inclusive than a simple dechlorination product. This chemically treats your tap water to detoxify nitrates, nitrites, ammonia, chlorine and sometimes chloramine.

The problem with dechlorination products and water conditioners is that they do nothing to remove the heavy metals and other dissolved solids, like iron and pharmaceuticals. Even though you may have great success using these types of products, what isn’t removed will accumulate in the tank.

Reverse Osmosis Is Best

The best and surest way your tap water will be safe for your saltwater tank is if you use Reverse Osmosis water. You can have this attached directly to your tap or you can get a setup just for your aquarium. This will offer the highest quality water possible for your tank, even if the municipal city water goes awry.

RO Control

This gives you the most control over your water quality. Depending on your test results, you can cater your RO system to suit your specific water issues. You may only require a three-stage filter, but more polluted city water may need a five- or seven-stage one.

Also, there are many systems available in aquarium shops, in-store and online, that offer specific RO systems just for your aquarium. These can be slightly less expensive than one for your home and less troublesome than traveling to your local water store.


It t may seem like a bit of an insurmountable conundrum to acquire the best water for your tank. But once you have a system in place, things should be smooth sailing. You want to strive for RO water filtration, but if that’s not feasible or far outside your budget, you can try to use commercial products.

Only use straight tap, filtered/purified or distilled water in case of an emergency or for a tiny top off. However, it may be better to get some kind of bottled water by a trusted producer. But only decide on a method once you receive solid test results to see what contaminants lace your tap water.

See Also:
How to Raise Phosphate in a Reef Tank
How Do You Test Fish Tank Water without a Kit?
How to Treat Ich in a Reef Tank with Garlic?
Why is My Fish Tank Filter Not Bubbling?
How Fast Do Cory Catfish Grow?