Service contracts are unsuitable if the main objective is to attract capital investment. The contracts may improve efficiency and thus release some revenue for other purposes, but the contractor is not under an obligation to provide financing. The effectiveness of the contractor may, in fact, be compromised if other sources of financing (from government or donors, for instance) do not materialize. The fact that the contractor's activities are discrete and segregated from the broader operations of the company may mean that there is no broader or deeper impact on the system operations, only discrete and limited improvements. The public sector remains in charge of tariff setting and assets, both of which are politically vulnerable and critical to sustain the system.