The quick sip of cool water from a garden hose on a hot day is a common summer memory, but the water flowing through that hose is often not as clean as the water from your kitchen tap. Standard garden hoses are not manufactured to the same safety standards as residential plumbing. This means the water can pick up contaminants from the hose materials and the environment where it is stored. The primary concern is not the source water itself, which is generally treated tap water, but the internal environment of the hose that introduces chemical and microbial hazards.
Chemical Leaching from Hose Materials
The majority of garden hoses are made from materials that can introduce compounds into the water, particularly when the water remains stagnant inside. Many standard hoses utilize polyvinyl chloride (PVC) as their main material. PVC often requires chemical additives called plasticizers to make the hose flexible and durable. The most common plasticizers are phthalates, chemicals that can leach into the water and act as endocrine disruptors.
These plasticizers are not typically used in indoor water supply lines, introducing a unique chemical exposure risk. Many vinyl hoses, including some brightly colored ones, have been found to contain heavy metals such as lead, which is sometimes used as a pigment or stabilizer. The brass fittings connecting the hose to the spigot can also be a source of lead, as they are not required to meet the same low-lead standards as residential indoor plumbing fixtures.
Studies show that water sitting in a hose, particularly one made of PVC, can contain levels of lead, phthalates, and Bisphenol A (BPA) that exceed drinking water limits. For example, BPA levels in hose water have been found to be up to 20 times higher than what the National Science Foundation (NSF) considers safe. This chemical transfer is accelerated by warmer temperatures, which increase the rate at which these compounds migrate from the hose material into the water.
Microbial Hazards from Stagnation and Heat
Beyond chemical contamination, a garden hose is an ideal environment for the growth of harmful microorganisms, especially when left outdoors and filled with stagnant water. The inside of the hose develops a slimy layer known as a biofilm, which is a complex community of bacteria and other microbes encased in a protective matrix. This biofilm provides a sanctuary for pathogens already present in the treated water supply.
When a hose is left lying in the sun, the temperature of the stagnant water inside can climb rapidly, often reaching 25°C to 45°C. This warm, dark, and still environment is a breeding ground for bacteria like Legionella species, the organism responsible for Legionnaires’ disease. The concentration of Legionella in hose water has been found to be comparable to concentrations seen in outbreaks associated with other water systems.
The presence of free-living amoebae further complicates the microbial risk, as these single-celled organisms can host and protect Legionella and other bacteria, shielding them from typical water disinfectants. When the hose is used, especially if it creates a fine spray or aerosol, these bacteria and their amoeba hosts can be inhaled, posing a health risk.
Practical Steps for Safer Water Use
If using a hose is unavoidable for tasks like filling a child’s pool or providing drinking water to pets, several steps can reduce the risk of contamination. The simplest measure is to flush the hose thoroughly before use, allowing the water to run for 30 seconds to a few minutes until it feels cool. This action removes the stagnant, warm water, which is highest in both leached chemicals and concentrated bacteria.
The best alternative is to purchase a hose specifically labeled as “drinking water safe” or “potable water safe,” which are typically white or blue. These hoses are generally made from materials like polyurethane or specialized PVC that are free of lead, BPA, and phthalates. They are often certified by organizations like NSF International, confirming that the materials meet strict health standards for drinking water contact.
For long-term protection, proper storage is recommended to minimize microbial growth and chemical leaching. Hoses should be drained after each use and stored out of direct sunlight, ideally coiled in a shaded area or a storage locker. Keeping the hose cool prevents the water from reaching temperatures that accelerate chemical leaching and pathogen proliferation.