If so what types of radiation does it block and how much water is needed to block each type.

Yes. Even light!

There are very many kinds of radiation, and there are a lot of differences in how well water will stop them. The easiest way for physicists to describe that is by naming the thickness of the layer you need to stop roughly 63%, so that 1/e = 1/2.71828... = roughly  37% passes through. If you stack 10x that amount, only 0.004% comes through. Another way to express it is the "absorbance", which is one divided by that characteristic thickness.

Let's start with the electromagnetic spectrum. There is a whole Wikipedia article about this that shows an excellent graph. In that graph you can see that the only electromagnetic radiation that can really pass through large thickness of water is visible light. Half of all blue/green light will pass through 50 meters of water. Half of red light through 20 meters. If you move into the ultraviolet, the absorbance really goes very high to, which means you quickly need only 0.01 micrometer of water to stop 63% of that radiation. For even shorter wavelengths, the penetration increases a little and you need thicker layers. On the infrared  absorption is more variable and a little less strong: you need several micrometers up to almost a millimeter of water to stop 63% there. And the thickness comes to roughly a cm if you go all the way to microwaves.

See:  Electromagnetic absorption by water

For alpha radiation and beta radiation, water is an excellent shield and you need a thin sheet. Neutron radiation is a bit more hard, you need thick layers to stop it all, but water is one of the best materials to do that.

See also:  Radiation protection (this mentions also more exotic radiation)

And:  Shielding of Neutron Radiation

Penetration of Different Types of Radiation

Alpha radiation, made up of helium nuclei, can be blocked by a sheet of paper, and by a film of water.

Beta radiation consists of either electrons or positrons. Positrons annihilate with electrons very rapidly, giving rise to energetic gamma rays. Relativistic electrons can pass through a significant amount of water before being decelerated to levels that do not cause radiation damage. Relativistic electrons passing through water generate Cerenkov radiation in the form of predominantly blue light, which is harmless. They tend to lose 2 MeV per centimeter of water penetrated.

Gamma rays can penetrate a moderate amount of water before being attenuated to the level of background radiation. They lose about half of their energy in penetrating 15 cm of water.

Neutrons can penetrate several feet of water.

Neutrinos could pass through a light year of water, but they cannot pose a radiation hazard except in the vicinity of a supernova or a neutron star collision.

Relativistic muons and pions can penetrate several kilometers of water. At lower energies they decay too fast to travel significant distances.

Water has no effect on gravitational waves, but they cannot be a hazard except in the vicinity of merging black holes and other high energy events where other hazards would be present long before the merger.

It does not block radiation. It can attenuate radiation, which is different. As a matter of fact, it is used in gamma food irradiators. Check this IAEA link

http://www-naweb.iaea.org/napc/i...

Water is the most convenient method to shield radiation when the source is not used. It would be complicated and expensive to use another container, for such a big composite source.

You mean radioactive rays?

For the three types normally cited, Alpha-, Beta-, and Gamma-rays the answer is mostly a question of the amount of matter between the source and the recipient. That's why we often use lead for radioactive shielding: it has a very high specific density. Gold would be even better, as it is heavier, but it is hellishly expensive.

But a thick layer of water works just as well as a thinner layer of lead. But your protective layer of water would have to be about 14 times as thick (lead is 11 times heavier than water, and heavy elements are slightly better than light elements for absorbing gamma rays, which are the most penetrating).

Then, in case of a nuclear explosion, there is a fourth type of radiation which is also very dangerous, and which water is very good at stopping: Neutrons. Neutrons do not interact electrically, and when they hit a heavy nucleus, they just bounce and continue with almost the same speed. But when they hit a light nucleus, such as the hydrogen in water, they slow down. As the hydrogen nucleus is about the same weight as the neutron, a lot of the momentum will be transmitted to the hydrogen nucleus (which is then braked by electrical forces), and a slow neutron is easily absorbed by another hydrogen nucleus, turning it into deuterium.

If you are getting more radiation from the potassium 40 in our bodies than we are getting from the source that we are shielding, we might as well stop shielding, I would think.

It looks to me like a foot or a little more of water reduces the dose from gammas by about nine tenths. 30 inches of water then is a factor of 100 reduction in gamma radiation. 60 inches is 10,000.

All the numbers are strongly dependent on the energy of the radiation - high energy gammas penetrate farther than low energy gammas.

Many universities have pool style reactors where you can look into the pool and see the reactor, see the blue glow of the Cerenkov radiation, safely while the reactor is operating.

Lots of good answers here - I just tried to fill in a gap or two.