Inequality of household water security follows a Development Kuznets Curve

Abstract

Water security requires not only sufficient availability of and access to safe and acceptable quality for domestic uses, but also fair distribution within and across populations. However, a key research gap remains in understanding water security inequality and its dynamics, which in turn creates an impediment to tracking progress towards sustainable development. Therefore, we analyse the inequality of water security using data from 7603 households across 28 sites in 22 low- and middle-income countries, measured using the Household Water Insecurity Experiences Scale. Here we show an inverted-U shaped relationship between site water security and inequality of household water security. This Kuznets-like curve suggests a process that as water security grows, the inequality of water security first increases then decreases. This research extends the Kuznets curve applications and introduces the Development Kuznets Curve concept. Its practical implications support building water security and achieving more fair, inclusive, and sustainable development.

Fig. 1. Three stages of Kuznets Curve research.

They are Kuznets Curve, Environmental Kuznets Curve, and Development Kuznets Curve.

Fig. 2. Inverted U-shaped relationship between site water security and the inequality of household water security within each site.

The inequality of water security was evaluated by a standard deviation (SD), b index of ordinal variation (IOV), and c polarisation (POL). Sample size = 28. The relationships were tested by quadratic regression models. A more stringent two-sided p-value threshold at 0.01 was used to counteract the potential problem of multiple comparisons. The three-figure panels demonstrate similar inverted U-shaped distributions (p < 0.001), suggesting a robust and consistent Kuznets-like relationship between water security and its inequality.

Fig. 3. Inverted U-shaped relationship between different water security and inequality indices.

Water security indices include composite WS score and the 11 comprising items, and inequality indices include SD, IOV, and POL. Sample size = 28. A more stringent two-sided p-value threshold at 0.01 was used to counteract the potential problem of multiple comparisons. n.s. denotes the quadratic regression model is not statistically significant while o.r. denotes the extremum point is out of the range of the available data. See Supplementary Table 4 for details.

Fig. 4. Relationships between income, socioeconomic standing, and water security at the site and household levels.

The upper row shows the site-level relationship (n = 24). INC, SES, and SWS denote income, socioeconomic standing, and water security at the site level respectively. The bottom row shows the household-level relationship (n = 5955). INC_h, SES_h, and HWS denote income, socioeconomic standing, and water security at the household level respectively. The relationships were tested by linear regression models and a two-sided p-value threshold at 0.05 was used. a Income vs. socioeconomic standing at the site level (Model 49). b Water security vs. socioeconomic status at the site level (Model 50). c Water security vs income at the site level (Model 51). d Income vs. socioeconomic standing at the household level (Model 52). e Water security vs. socioeconomic status at the household level (Model 53). f Water security vs income at the household level (Model 54).

Fig. 5. Five modes of sustainable development.

For each mode, example patterns of inequality at low, medium, and high levels of sustainable development are illustrated. Household water security is one aspect of sustainable development.