Seawater Delivery London: Natural Seawater to Your Door

Seawater delivery in London is available 7 days a week from Natural Seawater Supplier, based in Croydon, London, which delivers live natural seawater for marine aquariums across the UK and supplies UK fish stores. We deliver it ready to use, priced per order for your postcode, fill your containers or supply reusable food-grade ones, and can pump water straight into your aquarium, even in an upstairs flat.

This page is for London reefkeepers and marine fishkeepers who want to stop carrying drums home from the shop or mixing salt in a small flat. It covers how delivery works, how pricing is quoted, upper floors, regular orders, and why London’s hard tap water makes mixing your own harder than it looks. Ready now? Get a London seawater delivery quote.

Updated October 2026 by the Natural Seawater Supplier team.

Key takeaways

• Natural Seawater Supplier delivers live natural seawater across London 7 days a week from its Croydon base, ready to use with no mixing, priced per order by postcode.
• Natural Seawater Supplier fills your containers, supplies reusable food-grade 25-litre containers, or pumps water directly into your tank or sump.
• Thames Water states, as of October 2026, that all the water in its region is hard, so mixing your own saltwater in London depends on an RO/DI unit working hard.
• New customers of Natural Seawater Supplier can claim a free 25-litre trial of natural seawater.

How does seawater delivery in London work?

Seawater delivery in London takes four steps: quote, delivery method, day, then test and use.

1. Ask for a quote. Send your postcode, the volume you need and how often through the seawater delivery quote form, or phone us.
2. Choose how you receive it. We can fill your own clean containers, supply reusable food-grade HDPE 25-litre containers, or pump the water straight into your display tank, sump or mixing vat.
3. Pick a day. We deliver 7 days a week, so a Saturday or Sunday water change works.
4. Check and use. Test salinity, warm the water to tank temperature (usually 25–26°C) and do your water change.

The same service runs nationwide; our main aquarium saltwater delivery guide covers storage and how it compares with other options in more detail.

How much does seawater delivery cost in London?

Seawater delivery in London is priced per order: the total depends on your postcode, how much you order and whether you need containers, so we confirm the exact price in your quote.

Order	Natural seawater	Containers (one-off, if needed)
25 litres	Quote by postcode	1 reusable 25 L container
50 litres	Quote by postcode	2 reusable 25 L containers
100 litres	Quote by postcode	4 reusable 25 L containers
200 litres	Quote by postcode	8 reusable 25 L containers
Pumped straight into your tank	Quote by postcode	None needed

Containers are a one-off cost: you keep them and we refill them on later deliveries. For a fair comparison with mixing your own salt, see reef salt vs natural seawater.

Why does London tap water matter for a marine tank?

London tap water matters because, if you mix your own salt, every litre starts as tap water that an RO/DI unit has to strip back to almost nothing. The harder and more nutrient-rich the tap water, the more work that unit does.

London’s water is hard

As of October 2026, Thames Water says it sources about 65% of its water from rivers and 35% from underground, that the water passes through chalky limestone, and that “all the water in our region is hard”. On its own published scale, hard water is 200–300 mg/l as calcium carbonate and very hard is over 300 mg/l.

Parts of south London and Surrey are supplied by SES Water, which says in its water hardness guidance that much of its water comes from boreholes in limestone or chalk, that it softens the water slightly, and that hardness depends on where you live. Whichever company supplies you, your postcode report gives the exact figure.

Does London tap water contain nitrate and phosphate?

Yes: under the UK drinking water regulations, tap water in England can legally contain up to 50 mg/l of nitrate. Thames Water’s own London groundwater monitoring recorded raw, untreated nitrate of roughly 33–59 mg/l at its groundwater sources between September 2022 and August 2023, which it treats and blends to meet that limit. As typical industry practice, UK water companies also commonly add a small amount of phosphate to stop lead dissolving from old pipes. Safe to drink, but in a reef tank that is algae fuel.

What this means if you mix your own salt

• Hard, mineral-rich water exhausts the DI resin in an RO/DI unit sooner, so you replace resin more often.
• Once resin is spent, nitrate, phosphate and silicate slip through into your saltwater and feed green hair algae in a reef tank.
• Chlorine or chloramine must be removed by the carbon stage first, or it damages the RO membrane and reaches your tank.

Delivered natural seawater sidesteps these problems for water changes. Our water typically tests at nitrate 0–0.9, phosphate 0–0.05 ppm and ammonia 0. You still need a little RO/DI or pure water to top off evaporation, but far less than you would to mix every water change. Our guide to nitrate, phosphate and nutrient export explains why low-nutrient new water helps.

Parameter	Natural Seawater Supplier (typical)	Common reef target
Salinity	34–36 ppt	35 ppt (SG 1.025–1.026)
Alkalinity	7.5–8.6 dKH	7–9 dKH
Calcium	400–450 ppm	400–450 ppm
Magnesium	1250–1350 ppm	1250–1400 ppm
Nitrate	0–0.9 ppm	Low but not zero for most reefs
Phosphate	0–0.05 ppm	0.03–0.1 ppm
pH	8.0–8.3	8.0–8.4

Values vary slightly through the year. See ideal marine tank water parameters for how to test and what to aim for.

Can you deliver to a flat or an upper floor?

Yes, Natural Seawater Supplier delivers to flats and upper floors, and it is one of the main reasons London customers use us. Carrying 25-litre containers (approx. 26 kg each) up several flights of stairs every week is hard work. Instead, we can pump natural seawater directly into your display tank or sump, so nothing needs carrying. It works just as well for a third-floor flat as for a ground-floor fish room.

“I am up in a block of flats in canary wharf and driver always insists on bringing the containers up to me. Really good service.” Barry, from our customer reviews

When you ask for a quote, tell us your floor, whether there is a lift and how far the tank is from the door.

How do I set up regular seawater deliveries in London?

Regular seawater deliveries in London run as a standing order matched to your water change routine. As typical hobby guidance, a 10% weekly change suits most reef and fish-only tanks; our guide to how much and how often to change water helps you choose. Use your net water volume (display plus sump, minus rock and sand).

Net water volume	10% weekly change	Water per month	Containers per month
100 L	10 L	about 43 L	2 × 25 L
200 L	20 L	about 87 L	4 × 25 L
300 L	30 L	about 130 L	6 × 25 L
500 L	50 L	about 217 L	9 × 25 L

Each regular order is priced per delivery and quoted for your postcode. Setting up a new tank? Work out your first fill with how much saltwater you need to fill an aquarium; filling with natural seawater gives a new system a head start, as explained in natural seawater vs synthetic salt.

Looking for a marine aquarium supplier in Croydon?

Natural Seawater Supplier is based in Croydon, so south London is close to home, and we deliver across the rest of London as part of our nationwide UK service. If you are just outside London in Surrey, Kent, Sussex or Essex, see seawater delivery across the South East.

Frequently asked questions

Do you deliver seawater in London?

Yes. Natural Seawater Supplier is based in Croydon, London, and delivers natural seawater across London 7 days a week, as part of our nationwide UK delivery service. Send your postcode through the quote form and we will confirm the price and a delivery day.

How much does seawater delivery in London cost?

Seawater delivery in London is priced per order, based on your postcode, the volume of water and whether you need reusable food-grade 25-litre containers. You get an exact price when you request a quote.

Can you deliver seawater to a flat or an upstairs tank?

Yes. Natural Seawater Supplier can pump natural seawater straight into your aquarium or sump, which is how many customers in upstairs flats avoid carrying containers. Tell us your floor and access details when you ask for a quote.

Can I get a regular weekly or fortnightly delivery?

Yes, regular weekly or fortnightly seawater deliveries are available in London. Most London customers match deliveries to their water change routine, usually weekly or fortnightly. Tell Natural Seawater Supplier your tank volume and routine to get a suggested volume and delivery day.

Do I need my own containers?

No, you do not need your own containers. Natural Seawater Supplier can fill your own clean containers, supply reusable food-grade HDPE 25-litre containers that you keep, or pump water directly into your tank.

Can I use London tap water in a marine aquarium?

No, London tap water cannot go straight into a marine aquarium. Thames Water says all the water in its region is hard, and tap water also carries chlorine or chloramine, nitrate and phosphate. Tap water must be purified with an RO/DI unit before you mix salt, or you can use delivered natural seawater for water changes instead.

Sources

• Thames Water: Hard water
• SES Water: Water hardness and limescale (PDF)
• River Lea Catchment Partnership: Summer 2023 water quality update: London groundwater (PDF)

Bottom line

If you keep a marine tank in London, seawater delivery removes the two hardest jobs: carrying heavy containers and fighting hard, nutrient-rich tap water through an RO/DI unit. Natural seawater arrives ready to use, 7 days a week from our Croydon base, priced per order for your postcode, and can be pumped straight into your tank.