There are many decision support tools (DSTs) that can support water management and related decisions at farm, catchment, national, and international levels by farmers, policy makers, waterworks and other stakeholders. The different types of DSTs belong to different “families” for example the farm level tools that are developed to support farmers in production decisions and the catchment level tools that are developed to assist and inform policymakers at different levels on the likely outcomes of projects and policy actions to protect water.

We start by summarising findings from the literature was used to define criteria for what makes a DST within these different domains effective and of economic relevance.
»Previous evaluations of decision support tools
»Criteria for assessing the costs and benefits of using decision support tools

Six farm level DSTs were analyised according to these criteria.

• Mark Online, Denmark
• Plant Protection Online, Denmark
• Düngeplanung, Germany (Lower Saxony)
• Environmental Yardstick, Netherlands
• MANNER-NPK, UK
• Farmscoper, UK

All these DSTs have a factor in common, that the total costs of using the tools are kept low and that this is essential for a tool to be effective. The individual cost related to the use of a DST cannot be quantified as it vary substantial depending on farm scale, management practice, user habits, etc. However it was concluded that the farm level tool can save money for farmers if inputs are reduced, but also that they are important in meeting the cross compliance requirements that are compulsory in all EU countries. The farm level DSTs are not designed to rise environmental awareness as it is of no direct economic return to the farmer.
»Decision support tools at farm level

Two catchment level DSTs

• TargetEconN, Denmark
• Farmscoper, UK

were chosen as examples of catchment scale tools that model cost-effective solutions, that can be used for policy advice and management decisions. The evaluation indicates that significant resources can be saved by using such tools to reveal cost-effective solutions and management practices. The explicit modelling and inclusion of spatial data on agricultural production in both models allows for the identification of mitigation methods that can help to target pollutant reductions whilst not reducing food production. The catchment level models are also capable of assessing the effects of assumptions on the cost-effective solutions, and can therefore be used to assess the uncertainties associated with wrong or limited information.
»Decision support tools at catchment and national levels

Finally, there are DSTs to assess the benefits of water quality protection. Two different approaches are presented, and they can be used for general and more spatially specific assessments and measurements of the value of protection.

• MAES: Mapping and Assessments of Ecosystem Services. This is an European level decision support system (DSS) developed by the EU Commission, JRC (Maes et al 2012). Examples from implementation of a similar ecosystem services assessment tool in the Danish case study area in FAIRWAY, called MAES-DK, are used for illustration, as well as a similar example from the UK (The UK National Ecosystem Assessment, UK NEA (Bateman et al., 2011)).
• Meta analyses (benefit transfer) of valuation studies of water quality improvements: Two examples were chosen for illustration, namely:
  - An international groundwater valuation study applying meta-analysis (Brouwer and Neverre, 2018).
  - A Danish meta-analysis based on valuation studies from the Nordic countries, valuing water quality improvements using the Water Framework Directive classification of ecological status. Structure of the deliverable

The benefits measured by these methods can be used to make cost-benefit analyses of protection or other policy scenarios and decisions.
»Decision support tools for assessments of benefits

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