The KE of a particle is k = Mvc; where M = m/sqrt(1 - (v/c)^2). But when m = 0, no matter what the speed there is no KE by this equation. In other words, the physics, that there is no rest mass, disallows us from using the standard KE relationship.
But by experiment we know that E = hF is the total energy of photons with frequency F (h is a constant). And the total energy equation of a particle is E^2 = e^2 + k^2 where e = mc^2 is the mass.energy term.
And here's the deal. When m = 0, like photons, we see that e = 0 so that the particle energy equation collapses to become E = hF = Mvc = Mcc = Pc where P = hF/c is the measurable momentum of photons with frequency F.
In other words, as long as photons are going v = c the speed of light in a vacuum, they'll have no rest mass and their energy (which is all KE) is based on their frequency, not their speed.
And as I think about everyone here has rightly said, photons always travel at light speed c. The reason you hear of slower speeds through media is because that speed is an average speed, not the actual speed when the photons are moving within the media. And on average they move through media slower than through a vacuum because they are delayed a bit each time they collide with the atoms that make up the media.
Bottom line. The photons travelling through water are still rest massless. And just to blow your mind a bit, the photons that exit that glass of water are very likely not the same ones that entered that glass of water.