Time Crisis sounds familiar, but I never played it myself.
As for filtering radioactivity out of water, it could be useful in some situations. You don't become radioactive by being exposed to radiation, the radiation just kills or mutates cells (mutates as in possibly into cancer cells).
The only reason they use decontamination for people working with radioactive material is so they don't leave the lab or wherever with something radioactive under their fingernails or in their hair. This is a big misconception people have. Radioactivirty is a sort of decay, and it isn't passed on from one object to another.
Filtering the water could be useful if you were living at a safe distance from the water, but you had a pipe to provide water for drinking etc and that was the only available source. It also depends on the type of radiation too, there are three normal sorts:
Alpha, can't get through a sheet of paper and only goes a few cm through air so is only dangerous if exposed directly to skin or if breathed in, eaten or drank
Beta, Can be stopped by thin metal. Usually the most dangerous since it can get through your skinfrom the outside and kill cells in major organs
Gamma, can't be reliably stopped but most of it can be stopped by lead sheets. In high enough amounts can be dangerous, but usually would just pass straight through you without doing anything.
Radioactive material fires off particles of a certain type, or sometymes two types. These particles fly along until they hit something, and might or might not hit or simply pass through. How likely to hit rather than pass through it is is called how ionising it is, alpha is the most ionising and gamma the least by a long way. The chance of it hitting is also determined by the density of the substance, which is why lead is used for shielding. This explains why alpha particles can barely pass through a small space of air whilst it takes lead or thick concrete to (mostly) stop gamma. Concrete is used for fixed sites because it's cheaper than lead, but the lead is used for moving material because it's more compact.
cx2
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To live by honour and to honour life, these are our greatest strengths and our best hopes.