Peak Summer Water Deficit
A coastal town of 18,000 residents hosts up to 45,000 summer visitors in August. The water utility reports peak summer demand of 22,000 m³/day against reliable supply of 17,000 m³/day. Supply comes from three reverse-osmosis plants (11,000 m³/day) and groundwater abstraction (6,000 m³/day), but abstraction exceeds recharge and chloride levels in two boreholes have risen from 180 to 420 mg/L since 2015. Distribution leakage is 27% of input. Agriculture in the hinterland uses about 3,000 m³/day in summer, mostly from private boreholes. The utility proposes a fourth RO plant costing €28 million, producing 6,000 m³/day at 4.2 kWh/m³, with brine discharged through an outfall. Alternatively, a demand-management package would cost €9 million: leak reduction to 12%, smart meters, tariff reform, and reuse of 2,000 m³/day of treated wastewater for agriculture. The regulator requires a secure supply-demand balance by 2030 and compliance with the EU Water Framework Directive. The public opposes higher bills.
1. Calculate the peak supply-demand gap and the saving from the leakage target. Explain why the leakage saving alone cannot close the gap.
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Peak demand is 22,000 m³/day and reliable supply is 17,000 m³/day, so the gap is 5,000 m³/day. If leakage is 27% of the 17,000 m³/day put into supply, leakage is 0.27 × 17,000 = 4,590 m³/day. Reducing leakage to 12% gives 0.12 × 17,000 = 2,040 m³/day, a saving of 2,550 m³/day. The remaining gap is 5,000 − 2,550 = 2,450 m³/day. The saving alone cannot close the gap because leakage reduction depends on pressure, pipe condition and where the leaks are; not all saved water is available at the peak hour. The 2,000 m³/day reuse is for agriculture, so it frees some groundwater but is not all potable supply. A combination of measures is needed.
2. Evaluate the RO plant and the demand-management package, then recommend a sequenced plan.
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The RO plant adds 6,000 m³/day and would close the 5,000 gap with 1,000 m³/day reserve. Capital cost is €28m; energy is 6,000 × 4.2 = 25,200 kWh/day, and brine discharge creates marine impact. It can be built in roughly two to three years. The demand package costs €9m, saves 2,550 m³/day from leakage plus 2,000 m³/day from reuse, leaving about 450 m³/day; tariff reform and smart meters could shave the peak further. Cost per m³/day of capacity is about €4,667 for RO and €1,978 for demand management. Recommendation: implement demand management first, monitor the actual saving, then add a smaller RO plant or more reuse if the gap remains. Conditions: chloride monitoring, aquifer recovery, brine diffuser design and no new groundwater abstraction. This follows the precautionary approach and the Water Framework Directive.
3. The public opposes higher bills. How could tariff reform be designed to be fairer while still reducing peak demand?
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Tariff reform does not have to be a flat increase. A rising block tariff charges a low rate for essential household use and much more for high-volume use, such as filling pools or irrigating large gardens. A seasonal summer surcharge targets the peak when supply is tightest. A vulnerable-household tariff or credit protects low-income residents. Tourist accommodation and large users could pay a peak-season rate because they benefit from the summer economy. The revenue should be visibly linked to leak reduction and supply security, with published performance data. This design is fairer because it charges those who use most at the critical time, while still giving everyone a price signal to conserve. Consultation and a rebate for documented medical need reduce opposition.