Yes, koalas do drink water. They get much of their water from eucalypt leaves, but wild koalas also drink free water (Mella and colleagues, Ethology, 2020). This includes stemflow, the rainwater that runs down tree trunks. A 2025 Austral Ecology paper led by Connor Flanagan found stemflow is a safe water source for koalas.
Connor is an Environmental Consultant (Ecology) at ESEA. The paper is his research with co-authors from other institutions, not an ESEA project. It is a good example of the ecological research our team cares about.
Do koalas drink water in the wild?
For a long time, koalas were thought to get almost all their water from the leaves they eat. Observations of wild koalas have changed that view. A 2020 study by Mella and colleagues in Ethology described natural drinking behaviour in wild koalas at several locations in Australia and across a range of weather conditions. The authors suggested koalas may rely on free water more than previously thought.
The 2025 paper looks at one specific source of that free water, rain running down the trunks of trees.
What is stemflow?
Stemflow is the water that flows down the outside of tree stems during rain. Koalas have been observed drinking this water from tree trunks during rainfall.
Until this study, little was known about the properties of stemflow from the trees koalas drink from, or whether koalas choose particular trees for it.
What did the study find?
The study was carried out in the You Yangs Regional Park in Victoria. The researchers compared stemflow from trees that koalas were seen drinking from with stemflow from trees of the same species that koalas did not drink from. They looked at the volume of stemflow and its chemical and biological properties.
They found substantial variation in the solute concentrations and bacterial loads of stemflow between trees. Some of this variation could be explained by tree species and tree size.
Overall, the results suggest koalas drink stemflow opportunistically when it rains, regardless of its characteristics. The researchers found no evidence of koala pathogens, Cryptococcus species or Chlamydia pecorum, in the stemflow, and no potentially toxic levels of alkaline or heavy metals. They concluded that stemflow is an important and safe source of free water for koalas.
Why it matters for koala habitat
The authors note that climate change is making the koala’s environment increasingly water-limited, which makes the trees koalas drink from more important to understand. They recommend that future koala habitat protection policy consider the ecohydrological needs of koalas, and include stemflow as a key tree characteristic in habitat suitability mapping.
The paper also opens up research into how widespread stemflow drinking is across the koala’s range, and whether other tree-dwelling and threatened species do the same. For projects that need targeted species surveys or thermal surveys for koalas, it is a reminder that habitat value can depend on more than which tree species are present.
About the paper
Flanagan C, Krockenberger MB, Van Stan JT, Duffy J, and Mella VSA (2025). Koalas (Phascolarctos cinereus) and stemflow, drinking more than just water. Austral Ecology 50, e70076. https://doi.org/10.1111/aec.70076
Mella VSA, Orr C, Hall L, Velasco S, and Madani G (2020). An insight into natural koala drinking behaviour. Ethology 126, 858 to 863. https://doi.org/10.1111/eth.13032
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