The phrase "natural seawater" refers to water that is taken directly from the sea or ocean without any artificial additives or alterations. Full definition
It contains all essential major, minor and trace elements found in natural seawater. (petbusiness.com)
Prior to this discovery, many of the most abundant microorganisms in the ocean that have been successfully cultured were done so with the aid of natural seawater media. (sciencedaily.com)
Unless you are fortunate enough to live in one of the few areas of the country where natural seawater is available, you and your customers have to create your own ocean. (petbusiness.com)