Environmental impact of blue water use by adults aged 18-64 on the Island of Ireland

Blue water is sourced from rivers, lakes, and reservoirs and is used for drinking water, growing crops, and food production (1) . Approximately 75% of blue water use (BWU) comes from food systems (2) . Dietary change is necessary to meet net zero BWU sustainability goals by 2050 (3) . While there is some information on diet-associated BWU for the Republic of Ireland (ROI) (4) , BWU across the Island of Ireland is unknown. This study aimed to quantify the environmental impact of BWU of daily diets across adults aged 18-64 on the Island of Ireland, to determine population characteristics, nutrient intakes and key food sources influencing emissions. The Northern Ireland sub cohort of the UK National Dietary Nutrition Survey (2016-2019) (5) and the Irish National Adult Nutrition Survey (2008-2010) (6) were analysed. Information on food and nutrient intakes was extracted from four-day food diaries for a total of 1,484 adults aged 18-64 years. BWU values were assigned for each food (7) and the population was grouped into tertiles of low (T1), medium (T2), and high (T3) BWU. Differences in population characteristics, key nutrients (%TE or per 10MJ) and contributing food sources were examined across these tertiles. Statistical analysis was performed using chi-square and one-way ANOVA with covariates (age, BMI, Sex, Survey type and social class) and correcting for multiple comparisons as appropriate (P<0.001). BWU for the Island of Ireland was 481.9 ± 440.4 L/day, 524.7 ± 448.0 L/day for Northern Ireland and 474.9 ± 438.6 L/day for the ROI and 100% of the population did not exceed the BWU planetary boundary of ≤786 L/day (8) . Males had a higher contribution to the total BWU than females on the Island of Ireland (513.3 ± 482.2 L/day vs 453.2 ± 385.8 L/day). ‘Tea, coffee and water’ (76%), ‘rice and rice dishes’ (4%) and ‘fruit and fruit juice’ (2.5%) were the greatest contributors to BWU. When tertile analysis was performed, BWU from ‘tea, coffee and water’ was significantly higher for T3 at 837 ± 468.8 L/day versus T1 (57 ± 50.9 L/Day), this was similar for ‘rice and rice dishes’, where BWU in T3 was 26.3 ± 44.0 L/Day versus T1 (13.3 ± 25.2 L/Day). When nutritional analysis was performed, differences (P<0.001) across tertiles of BWU were observed for energy (11% increase between tertile 1 and 3), magnesium (12% increase across tertiles) and potassium (8% increase across tertiles). Overall, a shift to more sustainable diets is needed to prevent BWU boundaries being exceeded in the future. By filling a literature gap on the environmental impact of the Northern Irish diet, this study complements previous research on the ROI, offering a comprehensive view of the BWU footprint and providing a basis for the development of strategies to improve diet-related BWU on the Island of Ireland.