I would only put water in an emergency situation where I don't have coolant available. The coolant helps the engine to not overheat and to not freezing, while that could happen if you just use water. If you don't have your vehicle's manual to know the specification of the coolant, you can use the generally available Prestone and add water according to the table on the coolant's recipient. (or you can buy the pre-mixed formula)
Yes
Either condensation or someone put it there. Diesel can get into the coolant, but it won't happen the other way around.
water, anti freeze or coolant.
The water and coolant is put in the coolant reservoir for the location of this refer to the owners manual. It is best to do this when the engine is cold otherwise you run the risk of getting boiling water all over you. the mixture of coolant to water should be about 50/50.
If there is no risk of freezing , but it will weaken the strength of the antifreeze / water coolant mixture
coolant you retard not water!!
water will work until you can get proper coolant
Never put just straight water in your motor. You want to top off your radiator first then top off your coolant in the reservoir. Water will rust your motor from the inside out.
the coolant goes in the reservoir on the passenger fender. use a 50 percent water to 50 percent green coolant to fill it.
It is possible to put water only in the reservoir for coolant on a car. However, this should only be a temporary fix until it can be repaired by a mechanic.
If your car is leaking coolant get it fixed and put in the recomended coolant for your car. You should locate that info in the manual, also putting water in the winter is a bad idea since the water could freeze causing engine damage. I supposed you might be able to run it for a while in the summer with just water but get the leak fixed and put in the recomended antifreeze/coolant