Water is fine but it isn't going to degrease the chain or clean the oily dirt off it. I use a Chain cleaning tool to clean the chain on the road bikes but the MTB is covered and filled with greasy mud. Use the chain cleaner to get rid of the grease and oil and penetrate into the chain. Then hose off to finally clean. But you are then left with a Steel chain- filled with water that is going to go rusty. Water displacement oil to get rid of all the water- allow to drain and then lube.
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How long was I in the army? Five foot seven.
Spike Milligan