das Meerwasser
seawater
The salty water found in the world's seas and oceans.
Meerwasser ist wegen seines hohen Salzgehalts nicht als Trinkwasser geeignet.
Because of its high salt content, seawater is not suitable as drinking water.

seawater
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seawater
The salty water found in the world's seas and oceans.
Meerwasser ist wegen seines hohen Salzgehalts nicht als Trinkwasser geeignet.
Because of its high salt content, seawater is not suitable as drinking water.

'Meerwasser' (seawater) is a very clear compound. It is made up of 'das Meer' (the sea) and 'das Wasser' (water). So the meaning is quite literal: water from the sea.
Beim Schwimmen habe ich aus Versehen Meerwasser geschluckt.
While swimming, I accidentally swallowed seawater.
As a mass noun, 'Meerwasser' (seawater) is often used without an article when speaking about the substance in general. The article is only used when referring to a specific amount or type.
Meerwasser hat eine hohe Konzentration an Salz.
Seawater has a high concentration of salt.
Common collocations describe its properties or effects. Typical phrases are 'salziges Meerwasser' (salty seawater), 'kaltes Meerwasser' (cold seawater), or the statement that seawater is 'gut für die Haut' (good for the skin).
Viele Leute finden, dass Meerwasser gut für ihre Haut ist.
Many people find that seawater is good for their skin.
salt water
'das Salzwasser' and 'das Meerwasser' can both mean salty water. 'Meerwasser' is always water from the sea or ocean. 'Salzwasser' is more general: it can be seawater, but also water that salt has been mixed into, for example for cooking or gargling. That is why the words are easy to confuse if you are only thinking of salty water. If the origin is important, 'Meerwasser' fits. If only the salt content or a homemade salt solution is meant, 'Salzwasser' is better.

Das Meerwasser war im Sommer angenehm warm.
The seawater was pleasantly warm in summer.
Bei Halsschmerzen gurgelt Tom mit warmem Salzwasser.
When he has a sore throat, Tom gargles with warm salt water.