Can you top up a fish pond with tap water

Yes you can, but you will need to remove the chlorine from the tap water to make it safe for your fish.

When you fill a new garden pond for the first time you will more than likely use a hose pipe to fill it, this usually connects to your tap water supply which is full of chlorine, you then have to wait for a week or two before adding fish, this will allow the chlorine to evaporate which usually takes a couple of days and also allows the beneficial bacteria to grow in your filters.

Once you have an established pond you’ll find you will need to top it up from time to time, unfortunately at this point you can’t use water straight from the tap as you did when you first filled your pond.

Tap water has chlorine added to it to kill bacteria which are harmful to humans, although this makes it safe for humans, untreated tap water is very harmful to fish and plant life, it will also kill the beneficial bacteria from your filter system that are there to remove harmful toxins like nitrate and ammonia from your ponds water.

As we have said, chlorine is very harmful to fish, it can damage their gill’s, their scales and their breathing tissue, chlorine can kill fish, it burns them from the inside out so it’s not something to be messing a round with.

Can you dechlorinate tap water

Luckily there are ways of dechlorinating tap water.

The first and cheapest way is to fill buckets of tap water and leave them for a day or two, this will allow the chlorine gas to naturally evaporate from the water making it safe to add to your pond, you could even boil the water using a kettle or pot to speed up the process if you wanted to. This is fine for small ponds but will take lots of buckets to keep a large pond topped up.

The second and most common method is using a liquid dechlorinator, you simply add it to your pond every time you top up, this method turns tap water chlorine free within seconds, there are plenty on the market like Blagdon’s tap water fresh start from Amazon.

The third method is using an inline dechlorinator like this one from Amazon, these are great for large ponds or ponds that are fitted with an auto top system, it’s a device that fits between your garden hose and an outside tap, they use carbon to remove the chlorine, just turn on the tap and get instant dechlorinated water for your pond.

And finally you can plum in a filter system that uses replaceable filters to keep your pond free from chlorine, like this 3-stage system from Vyair which is available from Amazon, these are usually used for large ponds and are perfect for an auto top system. 

We would like to point out that rain water from water butts should be used with caution, you would think that topping up your pond with rain water would be safe, but although it will be free from chlorine it could still be contaminated with air born particles it picks up as it falls to earth, especially if it hasn’t rained for some time, rain water is also acidic which can alter your ponds pH balance.   

We have another article on how to remove chlorine here.

Chloramine in tap water

So far this article has concentrated on chlorine in tap water but there is another more deadly chemical when it comes to fish that is used to disinfect our tap water, that chemical is called chloramine.

For over a hundred years chlorine has been added to our water supply to kill bacteria, this has and still does work very well, but it doesn’t last long.

Over recent years some water authorities have started using chloramine in the water supply, although this is a lot better for us humans as it keeps the water disinfected for longer it’s a lot more dangerous to fish.

Chloramine is a mixture of chlorine and ammonia, normal chlorine is a gas that will evaporate in a day or two, but chloramine doesn’t work like a gas and can take a week or so to dissipate from the water.

As you can imagine this is devastating to your fish.

Can you remove chloramine from tap water

The good news is you can remove chloramine from your tap water.

The fill your bucket and wait a day or two that works for chlorine will not work as well, you would have to leave the water out for at least a week before adding it to your pond.

A liquid dechlorinator is a good way to remove chloramine but you need to use one thats specific to chloramine, Blagon sells an ammonia remover which also removes chloramine, you can buy it from Amazon.

If you’re not sure whether you have chlorine or chloramine in your water supply you can use something like this AquaSafe from Tetra which treats both, again you can buy it from Amazon or your local supplier.

Carbon will remove chloramine from the water, so you can use an inline dechlorinator like the one we have suggested for chlorine removal above or you can use the plumbed in filter system.

If you don’t know what treatments are used in your water supply you can as your local water treatment centre.

Why would you need to top up a garden pond with tap water

There are two main reasons why your pond would be losing water and need topping up, evaporation and a pond leak.

Evaporation is the easiest to solve, during hot spells water evaporates from your pond, this is normal, just use one of the methods above to top it up.

On the other hand if your pond has a leak it will be more difficult to solve.

You can use one of the above methods to keep the pond topped up but if the leak is near the bottom of your pond you will be fighting a loosing battle trying to keep your pond topped up with tap water if you don’t have an inline dechlorinator with an auto top up system in place, but it is possible to do until the leak is fixed.