Those expenditures that, once committed, cannot be (easily) recovered. These costs arise because some activities require specialized assets that cannot be readily diverted to other uses.

Urban planning that incorporates trees can have multiple benefits. Trees in urban areas have multiple benefits including increased infiltration and other benefits including shade and amenity value.
- Elaborated by NWRM project experts, validated by th European Commission

The cost linked the economic or relative scarcity of water once it is used.

Excavations, typically filled with gravel, designed to store water and allow it to infiltrate into underlying soils or aquifers.ﾠ Soakaways would typically receive point-source inflow (e.g. from roof drainage).ﾠﾠ
- Based on Stella definitions, adapted by NWRM project experts and validated by the European Commission

Traditional terraces consist of nearly level platforms built along contour lines of slopes, mostly sustained by stone walls, used for farming on hilly terrain.ﾠ When properly built and well maintained, terraces can reduce erosion and surface run-off by slowing rainwater to a non-erosive velocity.ﾠ So-called traditional terracing involves less disturbance of the terrain than modern terracing, as it does not involve significant levelling or cutting using heavy machinery.ﾠ
- Based on Stella definitions, adapted by NWRM project experts and validated by the European Commission

Afforestation of reservoir catchments can have multiple benefits. It can reduce sediment inputs from the catchment, lengthening the life of the reservoir, and may also have beneficial effects on water quality in some cases when peatlands are afforested. Afforestation can reduce peak flows and help to maintain base flows. The benefits of afforestation must be balanced against the potential for increased evapotranspiration from a rapidly growing forest.
- Based on Stella definitions, adapted by NWRM project experts and validated by the European Commission

Meadows are areas or fields whose main vegetation is grass, or other non-woody plants, used for mowing and haying.ﾠ Pastures are grassed or wooded areas, moorland or heathland, generally used for grazing. Due to their rooted soils and their permanent cover, meadows and pastures provide good conditions for the uptake and storage of water during temporary floods. They also protect water quality by trapping sediments and assimilating nutrients.
- Based on Stella definitions, adapted by NWRM project experts and validated by the European Commission

MAR is the purposeful recharge of water to aquifers for subsequent recovery and environmental benefit. Within the context of urban environment, MAR covers the injection and infiltration of captured stormwater ﾖ as such, it is linked to SuDS measures such as rainwater harvesting and infiltration techniques, but worth differentiating as a case where the primary purpose is to increase recharge to aquifers in addition to attenuating surface runoff,Mechanisms used to undertake the recharge should be highlighted. In this respect one can envisage:(i) surface structures to facilitate/augment recharge (such as soakways and infiltration basins);(ii) subsurface indirect recharge - artificial recharge is undertaken through wells drilled within the unsaturated zone;(iii) subsurface direct recharge - artificial recharge is undertaken through wells reaching the saturated zone.The regulatory approach to be adopted for each of the above three mechanisms could differ considerably, due to the fact that the level of natural protection to groundwater is vastly different for each of the mechanisms.
- Based on Stella definitions, adapted by NWRM project experts and validated by the European Commission

In the past, rivers flows have been modified through channelisation, embankments or modification of river beds. Those modifications were aiming at flood prevention or supporting changes of agricultural practices for example. This has led to uniformed flows in the rivers and often having effect on the water time transfers. Current practices for revitalisation of flowing waters are trying to create the conditions for diversifying the water flows, inducing more diversity in habitats for fauna but also increasing the water time transfers in order to prevent flash floods in the downstream areas for example.
- Based on Stella definitions, adapted by NWRM project experts and validated by the European Commission

Nitrate, NO-3, is the main nitrogen containing anion occurring in the soil. It is very soluble and moves freely in water through the soil profile. Nitrate in water is a pollutant above certain concentrations and can be a danger to human health. The main source of nitrate in water is agriculture although sewage discharges can also be an important factor.