Can tenants be forced to have liability insurance?

A dishwasher that's incorrectly connected and leaks, causing significant water damage, a pot left unattended on the stove, or a broken electric blanket – now the tenant's liability insurance needs to step in. But what happens if the tenant hasn't taken out such insurance?
Out of concern for substantial financial losses, many landlords require their tenants to take out liability insurance in the rental agreement and, to be on the safe side , to provide proof of such insurance.

However, most courts consider such standard clauses invalid, as the security deposit already provides sufficient protection. The Hamburg District Court, for example, also ruled that such a clause unfairly disadvantages the tenant and is therefore invalid (Case No. 48 C 602-97).

The situation is different with individual agreements, for which the legislator applies less strict standards. These individual agreements are provisions that are not a fixed part of a pre-printed lease agreement template, but have been negotiated separately with the tenant. Both parties must have made concessions. If the landlord has been obligated to take out liability insurance by means of an individual agreement, he can, if necessary, even be sued for fulfillment of this obligation.

However, proving the existence of an individual agreement becomes difficult. If it is included in every lease, it automatically becomes a standard clause and therefore invalid – even if the addendum is handwritten in every lease.