If a leased object contains a heat-intensive production unit, there may be optimisation potential if the lessor’s production facilities produce surplus heat, i.e. warm industrial or cooling water. The latter would have to be disposed of by discharging it into a river or the public sewage system and in compliance with a series of legal parameters. In particular the requirements concerning water quality (of the river water as well as the sewage water) listed in annexes 2 and 3.3 of the Waters Protection Ordinance. Despite the relief created by the revision of Annex 3.3 to the Water Protection Ordinance (in force since 1 July 2018), there is considerable interest in reducing the contamination of service or cooling water (for example in the form of high temperatures) in order to ensure its “disposal” and thus the own production process. Such a reduction in temperature can be achieved by utilising the surplus heat for the heating of a heat-intensive production unit, which – through suitable contractual stipulations with a heat contracting service provider – can significantly reduce the exposure to risk concerning the water protection legislation. Whether the heat contracting service provider should bear all of the responsibilities concerning planning, building and operating of a new energy conversion plant on the owner’s premises (plant contracting) or if the provider shall only be in charge of operating an existing plant (operating contracting) has to be examined on a case-by-case basis and will largely depend on the condition and the life span of the plant in question.