You can use water yes. Distilled water, through the brake booster line to intake, it virtually steam cleans and balsts everything in thier. As for the plugs, i use mopar combustion chamber cleaner once a year, on my 1995 neon, prior to changing plugs. Ive read form others, who have used seafoam, its realy jsut a mild detergent, in my opinion, but all recommended changing plugs after combustion chamber cleaning, just in case. Regular coppers go for just over a dollar anyways.