Inductively couple plasma mass spectrometry (ICP-MS) can be used to determine these metals int the water. You also can consult the following Ref.
Looi, Ley Juen, et al. "Baseline metals pollution profile of tropical estuaries and coastal waters of the Straits of Malacca." Marine pollution bulletin 74.1 (2013): 471-476.
Also you can go further on simultaneous speciation and determination of arsenic and chromium in water samples for instance, by high performance liquid chromatography with inductively coupled plasma mass spectrometry...