It is the landlord's responsibility to maintain the unit in a good state of repair, even if the tenant was aware of problems in the unit before they moved into it and the lease says that the tenant is responsible for maintenance. However, the tenant is responsible for keeping the unit clean, up to the standard that most people consider ordinary or normal cleanliness. The tenant is also responsible for repairing or paying for any damage to the rental property they caused or caused by their guests or another person living in the rental unit. Please visit the Ontario Landlord & Tenant Board for more information.