After having personally seen the seawater taken from some areas of Singapore... I can say that water taken at high tide facing the high seas, away from areas of little commercial activities or land construction activity or land fertilziation and not while it is raining would mean that the seawater is actually good enough to use for LFS operations and maybe even for reef tanks.
Of course, there may be some variations from the standard water parameters like PH, salinity, calcium and alkalinity in natural saltwater vs prepared saltmix and to a certain extent, risk from unwanted phosphates & other untestable pollutants etc.