## 1 Introduction  
Mountain tunnels are susceptible to water ingress, which can impede tunnel excavation progress and compromise the safety of the support system, leading to partial or complete failure. Water ingress is affected by geological structures such as weak zones, faults, and joints, which connect to aquifers [1, 2]. Sources such as joints (51%), faults (30%), pipelines (16%), and cavities (3%) contribute to a 45% disaster risk factor for water ingress in tunnels constructed using the drill and blast technique, such as the New Austrian Tunneling Method (NATM) [3,4]. In addition to geological structures, the inflow of water is influenced by the characteristics of the aquifer, drainage pattern, catchment area, and precipitation frequency. The presence of icicles, ice, and water ponding can further disrupt tunnel operations and pose safety risks [5, 6, 7]. Instances of such occurrences include the Beijing Metro Line 10 Tunnel, where equilibrium groundwater forced its accumulation, leading to a 24 m \(\times\) 14 m \(\times\) 12 m erosion, and the Chang-Ji Expressway and Taipei-Ilan Tunnels, where sudden groundwater inflow impeded excavation and led to collapse [8, 9, 10, 11]. Likewise, dynamic loads during seismic activity can also cause fractures in rock formations, which can provide pathways for water to enter tunnels. Additionally, seismic activity can cause ground movement, which can disrupt drainage patterns and increase the amount of water that flows into tunnels [12, 13, 14, 15]. To ensure the long-term sustainability of tunnel construction projects, it is critical to conduct both quantitative and qualitative analyses of the tunnel water [16,17]. While pre-grouting is effective in managing minor water ingress in tunnels, it is essential to carry out a thorough investigation and establish an efficient drainage system to handle significant water inflows. In cases where the water ingress is extensive, a combination of surface cleaning, grouting, and waterproofing methods are employed to restore the tunnel's structural integrity [4, 18, 19, 20, 21]. Damage to tunnels due to water seepage depends on the quantity and quality of water [8]. Concrete lining is carried out for strengthening tunnel walls and tunnel crowns to counter the water pressure and prevent water seepage and surface settlement in a tunnel [22]. Water in tunnels with an excessive amount of sulfate alters the composition of cement, weakens the bond between the aggregate and cement paste, and results in cracks [23,24]. In Switzerland, high chloride levels in the water continue to cause concrete to corrode [25]. Water infiltration in concrete structures can lead to the breakdown of its components, causing the growth of microorganisms that can induce the movement of foundations [26]. The presence of dissolved chlorides from sources such as deicing salts and seawater can permeate solid concrete and come into contact with steel, leading to corrosion in the presence of oxygen and moisture [27]. Similarly, the occurrence of chlorides and carbonates, along with a drop in alkalinity, can cause damage to the external bitumen layer and the ingress of dissolved gases. In addition to corrosion, metals may dissolve in water that is low in dissolved salts and high in specific ions, such as calcium, magnesium, sodium, and potassium [28]. Several instances of damage and corrosion in tunnels have been reported due to high levels of sulfate and acidic groundwater conditions, indicating the significance of water quality in maintaining the integrity of rock supports and concrete structures in tunnels [29,30]. The use of water from tunnels for domestic and agricultural purposes has been explored as a potential solution to water scarcity in certain regions [31,32]. However, due to the potential for the water to be contaminated with harmful substances, it is crucial to assess its quality before incorporating it into existing water supply infrastructure [33].