This is a case study about using nature-based solutions (NBS) for greywater treatment in the summer cottages of Norrtälje, a coastal municipality located in the Stockholm Archi-pelago, Sweden. Greywater is the domestic waste-water emerging from the bath, kitchen and laundry, and can be treated using conventional (non-NBS) as well as NBS technologies. This case study focused on the common NBS options available in the market. The stage of NBS for greywater in this case can be described as both planning and implementation. The NBS is planned or implemented at a decentralised (household) scale with property owners driving their own projects in individual capacities or in collectives. The results are based on an empirical study in Norrtälje Municipality that includes a literature review, survey and in-depth interviews with key stakehold-ers. From the case study it emerges that the NBS options are environmentally sustainable, helping jointly address the two major water challenges – quality and quantity, without producing any harmful residues from the treatment process. These also offer social and cultural benefits at the local scale (e.g., fulfillment of safe water needs, enriching the leisure environment) as well as providing participatory opportunities for local residents in sustainable environmental stewardship. Economically, these can enable cost savings in short and long-term as well as have potential for enhancing property values. An attempt was made in this study to understand the context of the decentralised NBS projects for domestic greywater treatment together with the pro-cesses of planning and implementation. The major opportunities and barriers in these processes were examined. Also, of interest was to explore the merits and drawbacks of the NBS options compared to the conventional (non-NBS) infrastructure available on the market.

This Case Study Brief is part of a Series of nine international case study briefs published under Project NATWIP. The Series is edited by Amy Oen and Sarah Hale, Norwegian Geotechnical Institute (NGI), Oslo, Norway.