Do koalas drink water? Science tells us they do!
For most of the twentieth century textbooks claimed that healthy koalas rarely drink because eucalypt leaves hold about fifty to sixty percent water and the animals recycle much of the nitrogen that other mammals lose in urine but a review of field notes and camera-trap footage collected between 2006 and 2019 overturned that view. We are learning more as the years go on.
Forty-six separate events showed wild koalas licking thin streams of rainwater that trickled down trunks and branches after showers. The behaviour occurred on winter nights near six degrees Celsius as well as on humid summer evenings above thirty. So it wasn't just weather-dependent.
The researchers have concluded that the long-held “no-drink” idea persisted only because koalas are nocturnal, high in the canopy and hard to watch, not because they are independent of free water (Mella et al. 2020; Mella et al. 2019).
At our Adelaide clinic we see the real consequences of koalas who are suffering in the heat. For some, lack of water is the reason for presentation. For others, their drinking is a symptom of illness. Read more to find out the difference because it is very important to know when a koala is just having a sip of water compared to when it is illness.
Do koalas REALLY drink water?
Koalas are often described as “leaf-drinkers” that seldom need a sip of free water. That story is fading as we learn more about these animals.
Over the past decade researchers have used camera traps, water chemistry tests and tiny body-temperature loggers to watch koalas more closely than ever. These studies show when and why koalas drink, how their natural “tree tap” system works, what happens during droughts and heatwaves, and how nearby water can tip the balance between life and death for this treasured animal. (Gardiner et al. 2023).
And if you want to know what koalas eat, then check out our page on "What Koalas Eat"
How do koalas drink from tree trunks?
When rain falls on a eucalypt, most people assume it just hits the leaves and drops to the ground. What actually happens is more interesting. A small but significant portion of that rainfall travels down the underside of twigs, collects on branches and runs down the trunk. Researchers call this stemflow and it turns out to be one of the main ways koalas access free water in the wild.
Not all trees are equal.
Smooth barked species like spotted gum Corymbia citriodora and lemon-scented gum C. maculata can channel more than five percent of a moderate rainfall event down their trunks. A stringybark with heavily furrowed bark diverts most of that water away from the trunk entirely. The bark type matters enormously.
To understand exactly how much water a koala might be accessing, researchers in 2024 and 2025 fitted sixty trees across four eucalypt species with sterile collars one metre above ground. The collars directed trunk water into chilled bottles to preserve the chemistry. Flow rates ranged from half a litre per hour on rough barked ironbark up to 4.3 litres per hour on the smooth gums koalas prefer for resting.
To put that in perspective, an adult koala weighing six to eight kilograms needs roughly fifty to one hundred millilitres of free water on a hot dry day.
A single hour of stemflow on a smooth barked gum can meet that requirement entirely. The study recommends that koala habitat assessments now factor in bark smoothness, branch angle and local rainfall patterns as direct indicators of water availability (Flanagan et al. 2025).
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What happens when koalas cannot get enough water?
During drought and extreme heat, eucalyptus leaves lose moisture. When leaf water content drops below about fifty-five percent of fresh mass, koalas begin showing signs of dehydration, higher blood salt levels and more concentrated urine. Their leaves are simply not providing enough.
An example where science investigated further.......
To find out whether supplementary water could help, researchers set up thirty-two water stations across two grazing properties in north-west New South Wales. Sixteen were ground level bowls and sixteen were tree-mounted troughs. Over a full year cameras recorded 2,452 koala visits averaging thirty-four seconds each. The warmer the day, the longer koalas stayed to drink, with visits increasing by around eleven percent for every five degree rise in maximum temperature.
Koalas chose the elevated troughs seventy-three percent of the time. Being up off the ground feels safer and that preference shaped the final trough design, a twenty litre food-grade poly container secured two to four metres up the trunk, shaded by a corrugated visor and refilled every forty-eight hours with a weekly clean. Flow meters recorded each koala drinking between eighty and one hundred millilitres per visit. Brushtail possums and sulphur-crested cockatoos used the troughs too.
The trigger for increased visits was clear. When leaf moisture dropped below fifty-five percent, nightly trough visits more than doubled. The koalas knew what they needed (Mella et al. 2019).
Another important reminder - A koala that drinks excessively is a sign of illness. This sort of drinking is different to what is described here. A small sip and then return to the trees is normal. A koala that drinks continuously needs vet assessment.
Rescue group details for South Australia are listed here
How do koalas cope in the heat?
During the record-breaking summer of 2023 to 2024, researchers fitted miniature data loggers to twelve wild koalas in northern New South Wales to track exactly how their bodies respond to extreme heat. Internal temperature was recorded every ten minutes while thermal cameras monitored behaviour in the canopy (Mella et al. 2024).
What they found was remarkable. The study identified four key things:
- Before sunrise on days forecast above thirty-eight degrees, each koala deliberately lowered its core body temperature from thirty-six degrees down to around thirty-two. Scientists call this heterothermy. By starting the day cooler the koala builds in a buffer, rising gradually through the morning without reaching dangerous levels until late afternoon.
- The cooling trick also conserves water. By reducing the gap between body and air temperature the koala needs less evaporative cooling, saving up to one fifth of the water it would otherwise lose through panting or licking its forearms.
- But heterothermy has limits. When temperatures climbed past forty degrees, two koalas left their resting spots and climbed down to drink from elevated troughs. Each drank around eighty millilitres. Leaf samples that day contained less than fifty-one percent water. The leaves alone were not enough.
- Koalas already dealing with urogenital chlamydiosis showed higher blood salt levels at the start of the day and visited water stations more frequently than healthy animals. Sickness amplifies the dehydration risk that heat creates.
Heterothermy buys time. It does not replace water.
As heatwaves become more frequent across South Australia and the eastern states of Australia, access to natural stemflow and well-placed supplementary water stations will matter more than ever for koala survival (Mella et al. 2024).
IMPORTANT: We do remind everyone that a koala that is seeking water and drinking a lot, should have a rescue group called - this koala most likely has a health condition that needs further investigation.
What this means for koalas in South Australia
The science is now clear. Koalas drink free water. The long held assumption that eucalyptus leaves provide everything a koala needs has been overturned. But in stating this important fact we do need to stress koalas in South Australia are prone to renal disease and drinking excessively is an early symptom. If you find a koala on the ground, drinking more than just a short sip, please call a rescue group. The koala could have a number of different health conditions needing urgent vet assistance.
Camera studies have documented koalas drinking from tree trunks during both winter nights and summer evenings. Smooth barked eucalypts can channel litres of clean water down their trunks after a single rain event, often more than enough to meet a koala's daily needs. When leaf moisture drops during drought or heatwave conditions, koalas actively seek out additional water. And even the koala's remarkable ability to manage its own body temperature has limits when heat is extreme and water is nowhere to be found.
Conservation planning should prioritise smooth barked eucalypt species. Landowners and councils in koala habitat areas can install simple tree mounted water troughs. Wildlife carers can offer water to koalas in distress knowing they are replicating something the animal would do naturally.
At our Adelaide clinic we believe good koala care starts with good science. The evidence is no longer ambiguous.
Koalas drink. It is time conservation decisions reflected that.
Finally, should you find a koala that appears heat-stressed, dehydrated or injured, do not attempt to handle or treat the animal yourself. Excessive drinking by a koala is not normal and needs further investigation by a qualified vet clinic.
Contact your local wildlife rescue organisation or veterinarian immediately.
See the story on what to do if you find a koala on the ground.
Disclaimer:
This article summarises peer-reviewed studies published between 2019 and early 2025.
New findings may refine or revise the conclusions.
Most research cited was conducted in eastern Australia (New South Wales and Queensland). Koala behaviour and water availability can differ in other regions, especially where rainfall patterns, tree species or disease pressures vary. South Australian koalas are very prone to renal disease and drinking excessively (polydipsia) is a critical symptom that needs a koala rescued.
In regards to water stations, installing or maintaining wildlife water stations should follow state regulations and best-practice guidelines developed by licensed wildlife carers, veterinarians and land-management authorities. Improperly designed drinkers can spread disease or attract predators. Artificial drinkers require regular cleaning (ideally ultraviolet or chlorine treatment) and secure mounting to minimise bacterial build-up and reduce the risk of transmitting pathogens such as Chlamydia pecorum.
Reference list
Flanagan, C., Krockenberger, M. B., Van Stan, J. T., Duffy, J. and Mella, V. S. A. (2025) ‘Koalas (Phascolarctos cinereus) and stemflow: drinking more than just water’, Austral Ecology, 50 (5), e70076.
Gardiner, R., Terraube, J., Frere, C. and Cristescu, R. (2023) ‘Roads and water availability influence the occurrence of koalas (Phascolarctos cinereus) in secondary habitat: a multiscale approach’, Biodiversity and Conservation, 32, 163–180.
Mella, V. S. A., McArthur, C., Krockenberger, M. B., Frend, R. and Crowther, M. S. (2019) ‘Needing a drink: rainfall and temperature drive the use of free water by a threatened arboreal folivore’, PLOS ONE, 14 (5), e0216964.
Mella, V. S. A., Orr, C., Hall, L., Velasco, S. and Madani, G. (2020) ‘An insight into natural koala drinking behaviour’, Ethology, 126 (8), 858–863.
Mella, V. S. A., Cooper, C. E., Karr, M., Krockenberger, A., Madani, G., Webb, E. B., Krockenberger, M. B. and Narayan, E. (2024) ‘Hot climate, hot koalas: the role of weather, behaviour and disease on thermoregulation’, Conservation Physiology, 12 (1), coae032.
Webb, E. B., McArthur, C., Woolfenden, L., Higgins, D. P., Krockenberger, M. B. and Mella, V. S. A. (2022) ‘Risk of predation and disease transmission at artificial water stations for a threatened arboreal folivore’, Wildlife Research, 49 (4), 324–334.