When it comes to big maintenance of a rental, the responsibility lies with the landlord. For example, he or she is responsible for taking care of repairing damages such as leakage, for maintenance of windowframes, replacing locks and doors or renovation of the facades. But also reparations such as replacing a broken heater, showerhead or toilet seat are the responsability of your landlord.
Small and daily maintenance, along with the repair of damages that you caused yourself, are the tenants' responsability. If the landlord also takes care of these small daily repairs, he or she is allowed to charge you in the form of service costs. However, this is only the case when you and your landlord discussed and agreed on this explicitly, usualy this agreement is part of your rental contract.