區域性多元供水系統之環境影響及效益評析

Abstract

在氣候變遷與水資源壓力日益升高的背景下，單一傳統自來水供水系統逐漸無法因應極端氣候所帶來的水量與水質衝擊，發展多元供水系統已成為全球趨勢。臺灣受限於地理與氣候條件，水資源調配困難，缺水風險日益嚴峻，促使政府積極推動再生水、海水淡化、聯通管等多元供水方案。然而，現行評估方法多著重於水量與建設成本，對於不同供水系統在水質提升與實質環境與社會效益之差異仍缺乏全面性探討。本研究以臺南地區為研究對象，應用生命週期評估結合模糊邏輯與水質指標，量化再生水、自來水、海淡水等供水系統在環境衝擊、水可用性與經濟效益上的表現。 研究首先以供應至用戶端每立方公尺水作為功能單位進行生命週期評估，分析系統在全球暖化、水消耗等18項衝擊指標下之環境影響，並進行情境分析以探討能源結構與管材使用年限對衝擊結果之影響。其次，結合Water Quality index (WQI)與模糊推論系統，依據農業、工業與民生三大用水需求，建構不同用途的水質功能性指標，進而推導水資源可及性剝奪指標(Water Availability Deprivation Index, WADI)，以彌補傳統水可用性及水稀缺指標未考慮水質之限制。最後，以缺水附加價值為基礎，量化水質提升對應之經濟效益，評估各供水系統在不同用途下的價值創造潛力。 研究結果顯示，再生水每立方公尺產水之全球暖化潛勢達1.95 kg CO₂ eq，約為自來水的10倍，主因為其高能耗與高處理強度。海淡水於18項指標中有9項環境衝擊最高，全球暖化潛勢高達3.64 kg CO₂ eq，為各系統之最。聯通管則因為管路建設耗用大量鋼材，在8項衝擊項目上為各系統中最高。自來水則受建設影響顯著，顯示傳統系統雖能耗較低，惟其基礎設施仍為重要衝擊來源。在水質功能性與可用性提升方面，WADI指標結果顯示再生水(WADI = -0.49)具最高水可用性改善幅度，反映其由低品質放流水提升至高適用性產水之能力。海淡水與自來水亦呈現可觀的水質改善效益，WADI分別為 -0.14與 -0.25。經濟效益評估顯示，再生水在民生與工業用途之每立方公尺價值提升分別達7,490元與7,395元，顯示其在水質提升對應價值創造上具高度潛力。 本研究提出結合水質功能性、水可用性與環境衝擊之整合性評估方法，建立WADI與價值提升估算機制，填補現有LCA方法中對水質應用價值考量之不足，提供決策者於供水政策、資源配置與永續管理上具體的量化依據。研究成果亦強調非傳統水源在水資源管理中之潛在角色，為未來建構具韌性與效益兼具之多元供水體系提供重要參考。

Under the growing pressure of climate change and global water scarcity, traditional single-source tap water systems have become increasingly vulnerable to disruptions in water quantity and quality caused by extreme weather events. The development of multi-supply water systems—such as reclaimed water, seawater desalination, and interconnecting pipeline—has emerged as a global trend. In Taiwan, geographic and climatic constraints have made water resource management particularly challenging, leading to severe shortages in recent years. Although government initiatives promote non-conventional water sources, current assessments mainly emphasize water quantity and construction costs, lacking comprehensive evaluations of water quality improvements and the associated environmental and socioeconomic benefits. This study focuses on Tainan City and employs Life Cycle Assessment integrated with fuzzy logic and water quality indicators to evaluate the environmental impacts, water availability, and economic benefits of reclaimed water, tap water, and desalinated water systems. Life cycle models were established using real operational data to quantify environmental impacts per cubic meter of water delivered, across 18 categories including global warming potential, water consumption. Scenario analyses were conducted to assess the influence of energy structure and infrastructure lifespan assumptions. Secondly, fuzzy water quality indices (FWQI) were developed for agricultural, industrial, and domestic uses using water quality parameters and fuzzy inference. These were aggregated into a Water Availability Deprivation Index (WADI) to capture water quality-related availability improvements often overlooked by conventional indicators. Finally, the economic value of water quality improvement was estimated using marginal value loss under scarcity, providing a monetary perspective on supply system functionality. Results show that reclaimed water emits 1.95 kg CO₂ eq per cubic meter—about ten times higher than tap water—due to intensive energy use. Desalinated water showed the highest impact in 9 of 18 categories, with global warming potential reaching 3.64 kg CO₂ eq. The interconnecting pipeline system demonstrates the highest impacts in several categories due to its heavy consumption of steel for pipeline construction. Tap water had lower emissions but significant infrastructure-related impacts. In terms of functionality, WADI values for reclaimed water (-0.49), tap water (-0.25), and desalinated water (-0.14) indicate reclaimed water provides the most substantial usability improvement, transforming low-quality effluent into highly functional water. The other systems also showed notable gains. Economic analysis revealed reclaimed water can generate NT$8,585 and NT$6,131 per cubic meter for domestic and industrial uses, respectively, underscoring its potential for value creation. This study proposes an integrated assessment framework combining water quality, availability, and environmental impact, incorporating WADI and economic valuation to address key gaps in conventional LCA. The results provide quantitative evidence for more sustainable, functionality-driven water supply planning and highlight the vital role of non-traditional sources in resilient water management.