Cisterns are used for both potable and non-potable purposes. Potable is another term for water that is clean and sanitary enough to drink. In addition, potable water can be used for cooking, cleaning, and bathing. Non-potable water includes the wide range of liquids that aren’t safe for these purposes. A non-potable cistern might contain anything from rainwater, with some latent background bacteria, to water that is heavily contaminated with sewage or chemical runoff. While both types of cisterns need liners to perform adequately, they require different materials. Find out how to match the ideal cistern liner to the purpose of the storage unit.
Lining Materials and Leaching
Since the liner used to seal or restore a cistern makes constant contact with the water stored with it, you must choose a material that won’t leach out anything unwanted. Some materials are far more likely to leach than others. Liner options also vary in their ability to provide proper sealing for more than a few years at a time. The options include:
- Metal liners like zinc or stainless steel. These rigid liners are tricky to insert into existing cisterns and tend to corrode faster than other materials. They’re unlikely to leach anything into the water unless they react to a treatment or purification chemical added to it.
- Flexible geomembranes made from the right materials. These materials are easy to fold and unroll as needed to fit inside a small cistern tank. They’re also easy to mount on the walls and floors of large cisterns. Potable and non-leaching materials like reinforced polyethylene (RPE) are available to maintain water quality.
- Hydraulic cement applied in a thin surface layer. This is an option for filling in large cracks and stabilizing degraded surfaces, but it’s too porous to serve as the primary liner. Pair cement surfacing with another type of liner to control seepage and leaks.
- Gel and epoxy coatings spread over the cistern’s interior surface. The liquid texture of these coatings allows for rapid coating, but it’s prone to forming invisible seams and cracks you can’t see. These coatings are also more expensive and less widely available than flexible geomembranes like RPE.
Reactivity with Non-Potable Water
In addition to leaching unwanted chemicals into a clean water supply, liners can also react with non-potable water. Reactivity leads to new gases and liquids forming that aren’t intended. This can shorten the lifespan of the cistern dramatically. Since most liners are added to extend the life of a cistern or restore it to use, reactions with the stored water will naturally interfere with this use. The stored water may also become unsuitable for the intended use after reacting with the liner. Look for geomembranes with little to no reactivity to restore an older cistern or to protect a new one. It’s not always easy to guess what dissolved minerals or compounds in a water supply might cause a liner to react. Materials like reinforced polyethylene (RPE) offer a broad range of chemical resistance, making them the best choice for any kind of cistern holding non-potable water.
Who Certifies Potable Water Safety for Liner Materials?
It’s important to choose cistern lining products that are certified as potable water safe. Many manufacturers claim to produce potable water safe geomembranes and cistern liners but don’t back up those claims with third party testing. The National Sanitation Foundation, now known as the NSF, is the best source for this kind of testing and certification. You’ll find that the best cistern liners are NSF certified with a clear rating to ensure you’re getting the potable water safety you want. For potable water requirements, the NSF requires a 61 rating. You may also see it listed as the ANSI 61 standard. No additives or stabilizers will leach into the water and cause safety issues, or reactions with purification chemicals, when used for long-term storage in cisterns.
Potable Water Plumbing and Fixtures
When designing a potable water cistern from scratch, you’ll need to do more than just select an NSF certified liner. The plumbing and other fixtures used to secure the attachments in place must also qualify as potable water safe. Many pipe fittings, pumps, and gaskets contain lead, plasticizers, or other chemicals that could affect the long-term safety of the water supply. Stick to potable water rated plumbing and pumps to ensure the entire cistern system remains safe to use for residential or commercial drinking water supply. A single, mismatched plumbing connection or fixture can throw off the certification of the entire system. If you’re planning on using a cistern as the only potable water supply for a home or business, you certainly can’t risk having the local health authority shut down your system over a plumbing mistake.
Final Use of Non-Potable Water
Even if you’re only handling a non-potable supply of water to irrigate a lawn or clean cars, the final use of the water should determine the quality of the liner. If you need to irrigate agricultural fields or water a backyard garden, you may want a potable water liner to ensure no chemicals leach into the water and accumulate in the soil. At the very least, ensure the liner is lead-free to avoid heavy metal build-up from long-term use. Don’t just consider whether the water is potable or non-potable when shopping for a liner product.
Turn to BTL Liners for help with lining tricky water cisterns. Whether you need a material that is appropriate for potable water use or any other type of storage, we can help. Our range of products boast high performance for both types of uses. Browse our website or contact our expert team today, to select the best liner for all kinds of cisterns.
