Forests worldwide provide a variety of ecosystem services including carbon sequestration, soil protection and water purification. In particular, the minimal use of pesticides and fertilizers in forest operations coupled with the tree root system are associated with higher drinking water quality. However, forest coverage is expected to have a more influential impact in groundwater quality rather than surface as well as, consequently, on drinking water treatment costs. This study uses cross sectional data at firm level to assess the marginal effect of forest cover on drinking water treatment costs for the case of Portugal, the first of its kind for the country. Our analysis makes use of a range of GIS and spatial variables which capture the heterogeneity in local forest coverage. The results obtained suggest the existence of a positive and significant effect of local forest cover on water treatment cost savings of 0.056%. However, this effect applies to firms extracting water from groundwater intakes. Neighboring measures of forest coverage have a greater impact on costs from surface water firms. The crucial role of local forest coverage through groundwater provision relates to a problem of intertemporal variation of those costs. Given the expected impact of climate change on precipitation in some regions where drinking water is mostly supplied by groundwater intakes, and since around 97% of forest land is privately owned, these results may suggest that appropriate incentives (e.g., payments for ecosystem services) could contribute to ensuring the sustainable use of water and forest resources.

全世界的森林提供各种生态系统服务，包括碳固存，土壤保护和水净化。特别是，在森林作业中最少使用农药和化肥以及与树根系统结合使用，可带来更高的饮用水质量。但是，森林覆盖率预计将对地下水质量而不是地表产生更大的影响，从而对饮用水处理成本产生更大的影响。这项研究使用公司层面的横截面数据来评估葡萄牙案例中森林覆盖率对饮用水处理成本的边际影响，这是该国的第一个案例。我们的分析利用了一系列GIS和空间变量，这些变量捕获了当地森林覆盖率的异质性。获得的结果表明，当地森林覆盖对于水处理成本节省0.056％具有积极而显着的影响。但是，这种影响适用于从地下水摄入中提取水的公司。邻近的森林覆盖措施对地表水公司的成本影响更大。通过提供地下水来覆盖当地森林的关键作用与这些费用的跨时变化问题有关。鉴于气候变化对某些地区的降水有预期的影响，这些地区的饮用水主要由地下水取水提供，并且由于约97％的林地是私有土地，这些结果可能表明采取适当的激励措施（例如，为生态系统服务付款）有助于确保水和森林资源的可持续利用。