Saudi Arabia has launched a nationwide Smart Water Metering (SWM) initiative addressing the critical challenge of water scarcity directly supporting the water sustainability goals of Saudi Arabian Vision 2030. This study develops a mathematical model for estimation of water consumption along with associated carbon footprint nationwide, across regions and demographic (Saudi and non-Saudi household) segments. Also, it demonstrates that water savings and carbon emissions reduction potential depends on two interdependent parameters such as user adoption rate and water system efficiency. The results reveal that conservational gains are mainly concentrated in regions of Riyadh, Makkah, and the Eastern Province accounting for 56% of total for Saudi households and 72% for non-Saudi households. Consequently, uniform nationwide rollout is identified to be extremely inefficient. Sensitivity analysis of scaled adoption rate from 25% to 100% shows that nationwide monthly water savings triples from 5.71 to 22.85 million m
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for Saudi households and from 2.19 to 8.76 million m
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for non-Saudi households respectively with proportional tripled carbon emission reductions. Similarly, increasing system efficiency from 70% to 90% results in a 42% conservational potential for both segments, highlighting the importance of quality water infrastructure. Finally, the Strategic Impact Matrix (SIM) combines these findings and shows that only the synergistic combination of high adoption rate and high system efficiency unlocks full conservational potential yielding around 4.6 times the water savings of the worst-case scenario. Also, it is found that partial strategies achieve only 8-72% of the full conservational gains. Consequently, a prioritized phased rollout of SWM is recommended. Phase 1 should target Saudi households in three high-impact regions covering Riyadh, Makkah, and the Eastern Province to achieve rapid and scaled outcomes. Phase 2 should target non-Saudi households covering same three regions leveraging population density for additional scaled impact. The approach of this study provides a replicable framework for maximizing water security, financial viability, and climate resilience for other regional contexts. Also, this study directly contributes to United Nations Sustainable Development Goals (UN-SDGs) Targets of 6.4 and 13.2.