There are a number of things that contribute to strokes. These include blood clots, aneurysms, air or plaque embolus, low blood pressure, and especially orthostatic hypotension, drug use, diabetes, high blood pressure; which can be caused from calcium among other things, head trauma, smoking, blood vessel constricting medications, tumors, polycythemia.......
One of the most interesting causes that are never really mentioned are the use of blood thinners. Especially coumadin (Warfarin) and heparin. These can both SIGNIFICANTLY increase the risk of strokes. But they will not mention this even in the PDR because they push these drugs to prevent strokes.
The best way to determine if someone may have had a stroke is to ask them to raise both arms. Asking them to smile is also good if they had problems lifting their arms before, or ask them to say a simple sentence. When a person has a stroke they generally will have some one sided paralysis which can be seen when you ask them to raise their arms or smile.
By the way, as with heart attacks a lot of the damage comes from enzymes released after the injury. It has been found that if ozone therapy can be administered within 3 hours of a stroke that all the symptoms from the stroke can generally be reversed. But again you only have that narrow window to work with.
I don't know if drinking water after a stroke would be a good idea. If there is paralysis then swallowing can be impeded and the water may end up in the lungs instead. This is why stroke victims in the hospital are generally given thick liquids only to make swallowing easier. The basis that water is suggested though is to help keep the blood from becoming too thick, which can increase the risk of stroke. But this is a good reason to stay hydrated to reduce the risk of stroking.
There is also a condition known as a transient ischemic attack. (TIA) or "mini stroke" in which there is no permanent injury to the brain. The person will develop stroke symptoms, but they generally only last a few hours. These can be great indicators for the risk of an actual stroke, but because of the short duration of symptoms people will often dismiss symptoms as being something else.