Green infrastructure, the use of soil, vegetation, and other natural landscape features to manage and treat water, is increasing in popularity as an alternative to traditional 'grey' infrastructure for water management. However, challenges arise to the widespread adoption of green infrastructure practices because of the difficulty in evaluating, accounting for, and valuing the benefits of such practices. Current accounting frameworks do not adequately account for the value of these assets, and the absence of appropriate accounting and evaluation tools may limit the ability of utilities to maintain or expand green approaches. 
This project developed two potential accounting frameworks to help water utilities assess and account for the ecosystem services provided by green infrastructure. The frameworks were pilot tested at three participating public wastewater and drinking water utilities over a period of five months to assess the benefits and feasibility of implementing national-scale accounting methods for green infrastructure. Several themes on green infrastructure accounting emerged from the pilot tests: the effects of regulatory vs. non-regulatory drivers, the importance of information flow both to the utilities from outside experts and within municipal government, and the need for standardized methods for assessing and accounting for the services provided by green infrastructure. Pilot test participants indicated that with further refinement of the accounting frameworks and the development of standardized guidance for valuing green infrastructure, national-scale implementation of these accounting frameworks is possible.
This report discusses the implications of larger-scale adoption and future research needs to facilitate green infrastructure accounting practices. U.S. cities are facing many challenges including aging water infrastructure and the costs associated with upgrades, changing weather patterns, rising demand for clean water, and more stringent water treatment standards. These pressures and others are affecting how municipal water utilities expand, repair, and maintain the infrastructure that carries and cleans our water. Building more grey infrastructure is the traditional approach to addressing these problems.
Some municipalities are, however, turning to green infrastructure as an option. These municipalities may be investing in green infrastructure directly for water utility management or indirectly by increasing their green space and greenways. No matter the original intent of the investment, green infrastructure may provide a cost-effective alternative that can help water utilities protect source water supplies, reduce stormwater runoff, and improve water quality. Current municipal accounting standards, however, do not adequately account for the benefits provided by green infrastructure. For example, the Governmental Accounting Standards Board (GASB), which establishes standard accounting practices for state and local governments, requires public utilities to value land assets using the historical purchase price, rather than the current market value and productive capacity. While there are good reasons to value assets at historical cost (such as avoiding over-valuation), this approach may also under-reflect the true asset value of many green infrastructure assets. Furthermore, the lack of a formal approach for accounting for green infrastructure and its benefits may be a barrier to further utility investment in this area and may predispose utilities to favor more investment in grey infrastructure. The lack of comparable accounting methods may also limit utilities' ability to convey green infrastructure's true benefits to ratepayers, policy...