Aquarium Saltwater Delivery UK: Natural Seawater to Your Door

Saltwater delivery means ready-to-use marine water brought to your door, so you never mix salt again. Natural Seawater Supplier, based in Croydon, London, delivers live natural seawater for marine aquariums across the UK, 7 days a week, and supplies UK fish stores. We fill your containers, supply reusable food-grade 25-litre containers or pump straight into your aquarium, and every order is priced by postcode and quantity.

This page explains how aquarium saltwater delivery works, how it compares with mixing your own or buying premixed saltwater from a shop, how much you will need for your tank, and how to store it. New customers can try 25 litres free.

Updated October 2026 by the Natural Seawater Supplier team.

Key takeaways

• Saltwater delivery brings ready-to-use natural seawater to your door, so there is no salt to mix, no RODI water to make and no 12–24 hour wait.
• Reusable food-grade HDPE 25-litre containers are available, or we can fill your own containers or pump water directly into your tank, even in an upstairs flat.
• Delivery runs 7 days a week across the UK and is priced per order; get a quote for your postcode and volume.
• Mixing your own salt with RODI water is cheaper per litre (approx. £3–£5 per 25 L as of October 2026) but needs an RODI unit, mixing kit and 12–24 hours per batch.
• New customers can claim 25 litres of natural seawater free.

How does saltwater delivery work?

1. Request a quote. Tell us your postcode, how much water you need and how often. Use our saltwater delivery quote form.
2. Choose how you want it. We can fill your own clean containers, supply reusable food-grade HDPE 25-litre containers, or pump the water straight into your aquarium or sump. Pumping is ideal if your tank is upstairs, for example in a third-floor flat.
3. Pick a delivery day. We deliver 7 days a week, so a weekend water change is no problem.
4. Use it straight away or store it. Check salinity, bring the water up to tank temperature, and it is ready for your water change.

We also supply UK aquatic shops, so you may already have used our water if your local fish store sells natural seawater.

How much does saltwater cost compared with mixing your own?

Delivered natural seawater is priced per order by postcode and quantity, while shop-premixed and home-mixed saltwater have the typical costs shown in the table (approx., as of October 2026; prices vary by brand and area).

Mixing your own is the cheapest per litre, and we would rather be upfront about that. What delivery saves is equipment, space and time. Making saltwater properly means producing RODI water, weighing salt, then heating and circulating it for 12–24 hours before testing. Public aquariums do the same on a huge scale: The Deep in Hull explains how it makes its own seawater from tap water, reverse osmosis and about 100 tonnes of salt a year.

Natural seawater or premixed saltwater?

Premixed saltwater from a shop is synthetic salt dissolved in RO water. It saves you mixing, but quality depends on the shop’s RO unit, salt brand and how long the water has been mixed. Natural seawater is real ocean water with natural trace elements and live bacteria and plankton. We compare the two properly in natural sea water vs synthetic salt mix.

Who uses saltwater delivery?

• Hobbyists doing regular water changes who want to skip mixing and keep parameters steady.
• New tank owners filling a whole system at once; mixing hundreds of litres yourself can take days.
• Reefkeepers switching from salt mix; our guide for reefkeepers switching to natural seawater shows how to do it without an alkalinity swing.
• Flat dwellers and anyone short of space who have nowhere to put an RODI unit and mixing vat.
• Aquatic shops that sell natural seawater to their customers.
• Anyone with a tank emergency who needs a large water change quickly.

Starting from scratch? Our saltwater aquarium guide for beginners covers costs and equipment.

How much saltwater do I need?

The amount of saltwater you need depends on your tank’s net water volume (display plus sump, minus rock and sand, typically 10–20% less than the glass volume). This table assumes a 10% water change every week, a good routine for most reef and fish-only tanks.

Prefer bigger fortnightly changes? 20% every two weeks uses the same water per month. For guidance on the right amount for your stocking level, read how often and how much water to change in a saltwater aquarium, and for the method, our step-by-step water change guide.

How should you store delivered saltwater?

• Keep containers sealed and in a cool, dark place such as a garage or under-stairs cupboard.
• Use within a few days for the most benefit from live plankton; stored well, natural seawater stays usable for several weeks.
• Before each change, test salinity and heat the water to tank temperature, usually 25–26°C.
• Never use containers that have held chemicals, fuel or detergent; food-grade HDPE is ideal.
• Discard water that smells of rotten eggs, which means it has gone stagnant.

Do I still need RO or RODI water?

Yes, you still need RO or RODI water with saltwater delivery, but far less of it. Delivered saltwater replaces the water you remove at a water change. You still top off daily evaporation with fresh RO or RODI water, not saltwater, because only pure water evaporates. Our guide to marine tank water parameters and top-off explains why.

Ready to try it? Claim 25 litres of natural seawater free as a new customer, then get a quote for regular deliveries to your postcode.

Frequently asked questions

Can you buy sea water for an aquarium?

Yes. You can buy natural seawater delivered to your door, buy premixed saltwater from a fish shop, or buy salt to mix with RODI water yourself. Natural Seawater Supplier, based in Croydon, London, delivers live natural seawater across the UK 7 days a week, priced by postcode and quantity.

How much does salt water cost per gallon?

Salt water typically costs about £0.91 to £1.45 per UK gallon as shop-premixed saltwater, or roughly £0.55 to £0.91 per UK gallon if you mix salt with RODI water yourself, plus equipment (approx., as of October 2026). Delivered natural seawater is priced per order by postcode and quantity, with no mixing or carrying. A quote shows the delivered price for your area and volume.

Where can I buy salt water for a fish tank near me?

Many aquatic shops sell premixed saltwater for collection. If you would rather not carry heavy containers, Natural Seawater Supplier delivers natural seawater across the UK 7 days a week. Request a quote with your postcode to check delivery to your area.

Can you pump saltwater straight into my aquarium?

Yes. Natural Seawater Supplier can pump natural seawater directly into your aquarium or sump as well as filling containers. Pumping is ideal for upstairs flats and large water changes.

Is premixed saltwater as good as natural seawater?

Premixed saltwater is synthetic salt dissolved in RO water, so its quality depends on the shop’s salt and RO unit. Natural seawater is real ocean water with natural trace elements and live bacteria and plankton. Both can keep a tank healthy if parameters are correct.

Is there a free trial of natural seawater?

Yes. New customers of Natural Seawater Supplier can claim 25 litres of natural seawater free through the free trial page on the website.

Sources

• The Deep, Hull: How we make our salt water

Bottom line

Aquarium saltwater delivery takes mixing out of your routine. Natural seawater costs more per litre than mixing your own, but you need no RODI unit, no mixing vat and no waiting, and you get real ocean water with every change. Get a quote for your postcode or start with a free 25-litre trial.