To waterproof an old bathroom with water leakage, start by inspecting for cracks, gaps, and damaged surfaces. Repair hairline cracks in walls or floors using epoxy or hydraulic cement. Apply a waterproofing membrane or tanking system to the substrate before retiling. Install a vapor barrier behind walls and seal all joints with silicone caulk. Use waterproof grout for tiles and reinforce shower pans with a linear drain. Test the waterproofing by filling the shower with water for 48 hours. For severe leaks, consider a professional assessment and installation of a tanking system or exterior waterproofing.

Old bathrooms often suffer from leaks due to aging materials, poor initial waterproofing, or structural shifts. Over time, tiles, grout, and mortar degrade, creating pathways for water. Data from the Environmental Protection Agency (EPA) shows that 95% of moisture-related damage in homes stems from leaks, with bathrooms accounting for 30% of cases. Leaks cause mold growth, which the EPA links to a 50% increase in respiratory issues in households. Financially, ignoring leaks can lead to $5,000–$50,000 in repairs, including mold remediation and structural repairs, per the Insurance Institute for Business & Home Safety (IBHS). Waterproofing membranes and vapor barriers create a physical barrier, diverting water to drainage systems. Studies show that properly installed tanking systems reduce leakage risks by 90%, while silicone caulk lasts 5–10 years compared to traditional mastics, which degrade in 1–3 years. Proactive maintenance, such as annual inspections and grout re-sealing, extends waterproofing longevity. Ultimately, combining material repairs with preventive measures minimizes long-term costs and health risks.