if the water is clean then you have got either one or both of your fill valves are leaking (like a dripping tap) into your machine. the best way to cure it is to replace them both. or if you want to identify which one (usually the cold) simply turn only one off overnight and work it out from there.
if the water is smelly then it's back filing from your sink waste.
solenoid valves are not expensive.
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