Fig. 4: Evaluation of six tanker market interventions until 2050.

Results from JWM-T simulations of six tanker market interventions for 2015–2050 (Supplementary Methods 5). a, Change in tanker groundwater abstractions. Large investments improving the public water distribution system or augmenting supply through desalination substantially mitigate the growth of groundwater abstractions for TWMs compared with a no-policy baseline. Under supply augmentation, tanker water abstractions still grow by +31% by 2050, compared with +64% under the baseline. Implementing both public supply investments simultaneously or TWM reform interventions (well closure, tanker license cap, household priority cap) stabilizes abstractions near average 2015–2020 levels until 2050. b,c, Public supply investments reduce substantial water vulnerability of households in 2050, defined as those receiving less than 40 l.p.d. (b), and largely prevent severe vulnerability in 2050, defined as those receiving less than 20 l.p.d. (c), by making piped water more accessible. Market interventions allow TWMs to mitigate vulnerability at rates similar to the baseline, with the exception of a substantial increase in severe vulnerability under a stricter enforcement of Jordan’s current well closure policy. d,e, Well closure also lowers the share of vulnerable households that enhance their water supply by purchasing tanker water in 2050 (d) and both well closure and the tanker license cap reduce vulnerable households’ average tanker water use in 2050 by about 50% (e). The household priority cap maintains tanker water use at levels closer to the baseline. f, Closing known illegal tanker wells raises the costs per cubic metre of water sold, compared with the baseline. The household priority cap provides a more efficient way of reducing groundwater abstractions, leading to lower costs. This also results in higher overall net benefits of tanker water provision (Supplementary Fig. 4). All monetary values are in constant 2015 US$. Asterisks (*) indicate non-applicable categories.