I have always used the cleaning solution (iRobot Hard Floor Cleaning Solution - CHF 14.90 fir 473 ml) or the water recommended by iRobot. If you google, you can see that some Braava m6 owners have also used other cleaners, while the cleaning solutions that are soapy, waxy or harsh (like bleach or ammonia) are not recommended. For alternative cleaning agents, I recommend consulting iRobot.ch for alternative cleaning agents so as not to destroy the warranty.