Ideally, they should be dissassembled and checked.
Some designs allow any water inside to move through the regulator with no damage and the air flow of the next dive will dry the interior. This is primarily the case with flow through balanced piston designs. But it is also important to note that this won't remove any salt inside the regulator. And as indicated above, you could get water in the SPG. In a mechanical gauge, this could cause a corrosion problem in the long term, but it can mean very rapid (and very expensive) failure in an air integrated computer.
Other designs can trap water in hard to reach places where it will not be readily removed by air flowing through the regulator. (unbalanced "flow by" piston designs are a good example). In addiiton, some balanced diaphragm designs can be damaged by having a more or less incompressible substance in them. So the safeest approach is to have a tech dissassemble it, dry it and clean it.
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Someone above advised taking the cover and diaphragm off of a second stage to clean the inside of the regulator. This can be problematic as one of the more common causes of a flooding or wet breathing second stage is an improperly seated diaphragm. So you are potentially causing a bigger problem than you are solving.
If used regularly, and rinsed properly a second stage will not accumulate significant amounts of sand, silt, etc.
Also, attempting to re-seat a wet diaphragm in a wet second stage is one of the leading causes of having of having a diaphragm seat improperly as it may slide off as you screw the purge cover back on. If you remove the diaphragm be sure you know what you are doing and know how to test the reg to ensure the diaphragm is properly seated.
