Pond liners typically last between 10 to 40 years, depending on several factors such as the material, installation quality, environmental conditions, and maintenance. 
1. **Material**: 
   - **EPDM (Ethylene Propylene Diene Monomer)**: Known for its flexibility and durability, EPDM liners can last 20 to 30 years. They are resistant to UV rays and temperature fluctuations.
   - **PVC (Polyvinyl Chloride)**: Generally less expensive, PVC liners have a lifespan of 10 to 15 years. They are less durable than EPDM and can become brittle over time.
   - **HDPE (High-Density Polyethylene)**: These liners are robust and can last 20 to 40 years. They are resistant to chemicals and punctures but are less flexible, making installation more challenging.
   - **Butyl Rubber**: Similar to EPDM, butyl rubber liners can last 20 to 30 years. They are highly flexible and durable.
2. **Installation Quality**: Proper installation is crucial for maximizing the lifespan of a pond liner. Ensuring a smooth, debris-free surface and using an underlayment can prevent punctures and tears.
3. **Environmental Conditions**: Exposure to harsh weather, UV radiation, and fluctuating temperatures can affect the longevity of pond liners. Liners in shaded areas or those protected by a layer of rocks or plants tend to last longer.
4. **Maintenance**: Regular maintenance, such as removing debris, preventing plant roots from penetrating the liner, and repairing any small tears promptly, can extend the life of a pond liner.
In summary, the lifespan of a pond liner is influenced by its material, installation, environmental exposure, and maintenance practices. Proper care and installation can significantly extend the life of a pond liner, ensuring it remains functional for many years.