Is water actually blue or is it transparent?
It is blue. But white light needs to cross a long distance through the water to actually get the blue tint.

This related question explains it for ice, but for water it is pretty much the same story.

This article, mentioned by @JeopardyTempest in the comments of the answer to the above question, tackles the case of the oceans. There it says:


  The ocean looks blue because red, orange and yellow (long wavelength
  light) are absorbed more strongly by water than is blue (short
  wavelength light). So when white light from the sun enters the ocean,
  it is mostly the blue that gets returned.