Outdoor tap

If you own a garden pond, we know that you will appreciate just what a delicate ecosystem it can be. It is therefore vital that when it comes to the time to clean or refill your pond, you provide just the right balance in the water for the wildlife to thrive. Of course, one of the easiest things would be to use water right out of the tap; but can you fill your pond with tap water?

Tap water may contain higher levels of chlorine owing to the way that your water company treats it before delivering it to you. This is excellent news for humans since it means that any harmful bacteria would have been removed and the water is fully potable. However, for your garden pond, these high chlorine levels might not be quite as beneficial and will likely kill off any good bacteria that help the ecosystem thrive.

But we know what you are thinking; if you can’t simply turn on the tap to fill the pond, what are you meant to do? The good news is that you can use tap water, provided that it is dechlorinated first. In this guide, we will be showing you the best way to do this.

Can I Use Rainwater?

Some people may think that using rainwater to fill your pond removes the risk of chlorine. However, while it can often be pure, most rainwater may not be as pure as many people would imagine. Once it falls from the sky, any surface it touches poses a risk of contamination which, if used to fill your pond, could cause all sorts of problems. For this reason, if you do collect rainwater, we would still urge you to consider one of the methods we will be discussing in the following sections.

Ways To Make Tap Water Safe For Your Pond

It might seem as though treating your tap water before you can use it in your pond is something of a headache. However, there are several methods that you can use that are simple and don’t require as much input as you may have first imagined. But before we look at these methods, we should also consider that when installing a new pond, you will need to encourage bacterial growth.

Often referred to as new pond syndrome, ponds that are green, ridden with algae or high levels of ammonia or nitrates will more than likely have an imbalance owing to the water that has been added. In this case, wildlife and fish can become very stressed and you certainly won’t have the pond of your dreams.

This happens because the water in the pond has not had a chance to develop the good bacteria it needs, especially if chlorinated tap water has been added which will have killed any existing bacteria in an established pond. The only way to counteract these problems is to mature the bacteria over time which, in essence, means that you will need to employ a little patience.

Let The Water Sit

One of the most common methods for encouraging beneficial bacteria growth in pond water is simply to allow it to stand overnight. This process is known as gassing off and relies on the water losing its chlorine before being added to the pond. This is possible because chlorine is a gas and, when the water is left to sit out, this gas will naturally disperse.

However, you might need to check what products your water company uses. While many still use chlorine, there are some that use a chemical called chloramine which does the same job but not being a gas, will not disperse in the same manner.

Use A De-chlorinator

A de-chlorinator is a substance that is used to remove chlorine from the water and typically, there are two different types; a liquid de-chlorinator and an inline de-chlorinator. Either of these methods is suitable for pond water and which you choose will mainly come down to personal preference. However, it is worth keeping in mind that if you have a koi pond that requires serious amounts of water, an inline de-chlorinator might be a better option.

Liquid Dechlorinators

Liquid de-chlorinators (amazon link – opens in a new tab) are considered to be one of the easiest ways of preparing your tap water to go into the pond. It is merely a matter of pouring the liquid into the water and allowing it to do its work. However, you will need to consider the size of your pond as not adding enough won’t have the desired effect.

The details of how much you will need to add will be given on the bottle. In addition, you should also think about how much tap water you are adding. For example, if you are cleaning your pond and only removing half of the water, when you re-add that half, you will only need to add the corresponding amount of liquid de-chlorinator.

Let’s assume that the pond is 1000 litres and you remove half of the original water. In this instance, you would only need to use treatment for 500 litres. When doing this, we would advise adding the de-chlorinator to the remaining water before turning on the tap and topping up, this way, none of the new water will adversely affect the pond.

Once added, you will simply need to give it a bit of a mix. One of the best things about this is that the results are instant; as soon as the solution is mixed in, the water will be free from chlorine.

Going back to chloramine, if this is something your water company uses, this method is suitable since many liquid de-chlorinators are made to break down this chemical too.

Inline De-chlorinators

An inline de-chlorinator (amazon link – opens in a new tab) is installed between your tap and the end of your hose. As the water passes through the de-chlorinator, it is treated before moving on into your pond. This type of de-chlorinator works using carbon which, as the water passes through, effectively removes any chlorine. For larger ponds, these can be much more convenient and efficient.

However, one thing that you should keep in mind is that this type of de-chlorinator will have a limit as to how quickly the water can pass through. This flow rate will be given when you buy the product and should always be adhered to. It is also important to look at whether the carbon block needs replacing as some products are disposable while others require the block to be replaced once it is spent.


Filling your pond requires a very large amount of water, for some people, this could be hundreds or even thousands of litres. Therefore, one of the most convenient ways to top it up is to use your tap water supply. However, since this contains chlorine, it may result in an imbalanced pond.

The good news is that you can use tap water in your pond but you will first need to take the chlorine out. This can be done in several ways but most commonly will require a de-chlorinator or for the water to be left to gas off for 24 hours.

Garden Doctor Trev

Garden Doctor Tips

“If you are unsure of what is in your water, chlorine testing kits are available!”

“Even trace amounts of chemicals can result in an imbalance that could be devastating!”

“Check if your water supplier uses chlorine or chloramine!”

“Dechlorinating your water is imperative as chlorine is toxic and will harm your wildlife!”

Frequently Asked Questions

Can I use tap water for my Pond?

Ponds are a great addition to any backyard or garden. They can provide your family with hours of enjoyment and relaxation, as well as adding a natural touch to the landscape. If you intend on keeping fish in your pond, then it is critical that you use only clean water for them to live in. Tap water contains chlorine which will kill all living things in your pond – including plants and animals – this makes it very important to remove the chlorine immediately. 

Will Tap Water Kill my pond fish?

Chances are that you have pond fish living in your backyard. They might be goldfish, koi, or any other type of pond fish. The most important thing to remember is that the water they live in should not come from a tap. Tap water contains chlorine and other chemicals which can kill your little friends!

If you do use tap water, ensure that you remove the chlorine immediately!

How long do you leave tap water before adding fish to a pond?

Most people who have a pond or water garden will want to know how long they should leave the tap water before adding fish. The answer depends on the type of filter and pump that you are using, as well as your climate and geographical location. For most ponds, it is advised that you let the water sit for at least 2-6 weeks before introducing any fish. This will allow time for chlorine levels in the water to lower, which can affect their health if introduced too soon.

This process can be sped up by treating the water with a de-chlorinating solution.

About Me

Hi, I’m Trev and I’ve been growing things since I can remember. When I was younger, I grew up on a farm, so I have always been around plants and animals. After studying horticulture at university, I decided to start my own nursery which I have run now for 25 years. In my spare time, I run this website – which is a resource for people who want to learn more about their gardens.

More You Might Like