Many people, after purchasing and drinking bottled water, habitually reuse the plastic bottles that held the water for convenience—to carry drinking water in their cars or while working outside. However, this is not a good idea.

Generally speaking, polyethylene terephthalate (PET), a material found in some plastic bottles and containers, has been found in recent studies and inspections to contain a potential carcinogen: diethylhydroxylamine (DEHA). For safety reasons, these plastic bottles or containers should be used only once. If longer-term use is necessary, one week is the absolute limit, and they should not be used to hold hot drinking water or food.

Repeated washing and rinsing of plastic bottles or containers can cause the plastic to break down and release carcinogens, which dissolve into the water inside and, when ingested, can cause irreversible, permanent damage to the body.

When selecting a water bottle, choose reusable plastic bottles, glass bottles, or bottles with stainless steel liners. Be sure to wash them thoroughly after each use to prevent bacteria from breeding in warm, damp bottles.

When purchasing water bottles, consumers should make rational choices based on logic and science, and avoid blindly trusting exaggerated claims in advertisements about health, safety, or “magical” designs.

By Michael Chiu, MWS, CI
Previously published in Ming Pao Daily News – Updated and Revised in 2026