Yes but you need to treat the tap water first

If you’re using tap water to mix artificial seawater or replace water lost through evaporation in your lobster tank there are a couple of things you need to be aware of. Tap water in the UK is usually treated with chlorine or chloramine to make it safe for drinking. Both can cause problems for live shellfish and the biological filtration system so it’s important to remove or neutralise them before adding the water to your tank.

What’s the difference between chlorine and chloramine?

Chlorine and chloramine are both used to disinfect drinking water but they behave quite differently.

Chlorine can dissipate from water when it’s left standing. In our original video Keith explains that this can take around 24 to 36 hours. However the time will depend on the water conditions and it’s important to check that the chlorine has gone rather than simply relying on the time.

Chloramine is more persistent. It’s a compound formed from chlorine and ammonia and doesn’t readily evaporate from water in the same way. It can remain present for considerably longer which means leaving a bucket of water standing overnight isn’t a reliable way of dealing with it.

How do you know if your tap water contains chloramine?

Your local water supplier should be able to tell you whether chlorine or chloramine is used to treat your drinking water. However water treatment practices and water quality can vary.

Rather than worrying about which disinfectant is present we recommend treating tap water to deal with both chlorine and chloramine before using it in your shellfish holding system.

It’s a simple precaution which helps protect your shellfish and the beneficial bacteria in your biological filter.

How do you remove chlorine and chloramine from tap water?

The simplest approach is to use a suitable water treatment product which neutralises chlorine and chloramine.

Products such as Optimus and Seachem Safe are examples of treatments designed for this purpose. Follow the manufacturer’s instructions and make sure the product is suitable for your intended use.

Once the tap water has been properly treated you can use it to mix artificial seawater or replace water lost through evaporation.

Remember that when you’re replacing evaporation you normally add treated freshwater rather than more saltwater. The water evaporates but the salt remains in the system.

What does activated charcoal do in a lobster tank?

Activated charcoal is another useful part of water treatment and filtration.

Activated charcoal helps remove chlorine from water. It can also help break down chloramine although this can release ammonia which then needs to be dealt with by the biological filtration system.

This is one of the reasons we include activated charcoal in the filter socks within our Lobster Pod and Crab Pod systems.

However we would still recommend treating tap water before adding it to your holding system rather than relying on the activated charcoal in the filter to do the job.

Why is untreated tap water a problem for biological filtration?

The biological filter contains beneficial bacteria which convert ammonia into nitrite and then nitrate. These bacteria are an important part of maintaining good water quality in a recirculating seawater system.

Chlorine and chloramine are used in drinking water because they kill or control microorganisms. Unfortunately they can also affect the bacteria we rely on in biological filtration.

Adding untreated tap water can therefore create problems for both the shellfish and the filtration system.

What’s the best way to prepare tap water for a shellfish holding system?

If you’re using tap water to make up artificial seawater or top up your Lobster Pod or Crab Pod we recommend treating it with a suitable chlorine and chloramine neutraliser before use.

Check that the treatment has worked and make sure the water is suitable for your system before adding it. When preparing artificial seawater you’ll also need to check the salinity and temperature.

It’s a relatively simple job but an important one. A little care when preparing your water can help avoid problems further down the line.

Last Updated November 2026