As the name suggests, third-party access involves a party other than the incumbent service provider and infrastructure owner gaining access to and using excess capacity in the natural monopoly infrastructure of the incumbent (AGD of PMC August 2006: 13).^[11] The purpose of the access is to promote competition in markets upstream or downstream of the relevant infrastructure.^[12] Of course, the service provider could contract with the third-party access seeker to grant that access, but the provider may be unlikely to do so where the third-party proposes to compete with the service provider in the upstream or downstream markets. Certainly, the infrastructure owner possesses the unilateral capacity at general law to refuse access. The purpose of the statutory third-party access regimes is to facilitate such access and to provide a framework for an independent agency to arbitrate the terms of third-party access in those cases where the incumbent and the third party or parties cannot agree the terms of access. The presence of the statutory access regime would, no doubt, set the framework for any private access arrangements and may even be preferable for the incumbent service provider because it can provide procedural certainty.

As a result of the infrastructure access, the new entrant would be in the position to target new customers or the incumbent’s existing customers and provide them with an established service, such as water supply or sewage removal. Alternatively, the third party could supply a new service as a result of gaining access. An example of the latter would be a third party supplying a water-recycling service as a result of gaining access to the incumbent’s wastewater system^[13] (AGD of PMC August 2006: 13). This has become known as ‘sewer mining’.