There is a considerable amount of misunderstanding on the subject of the water requirement of tortoises. This is unfortunate, as a number of very serious pathological conditions are directly related to the availability or otherwise of environmental water, and to the general hydration status of reptiles such as tortoises.
The most common health problems associated with a sub-optimum level of hydration or prolonged period of environmental water deprivation include an accumulation of solidified uric acid in the renal system and bladder; articular gout; and kidney failure. All of these are extremely serious conditions and it should be noted that dehydration, even for short periods, can have grave long-term consequences.
Terrestrial chelonians, lizards and snakes excrete nitrogenous waste products including ammonia (which is produced as a result of the protein metabolism) in the form of uric acid. Should the animal suffer dehydration, the nitrogenous waste metabolism is the first major function to suffer. Tortoises cannot concentrate urine in the same way that mammals can, so they cannot eliminate dissolved metabolic wastes such as ammonia and urea without losing a considerable volume of water. This is not important to aquatic or rain forest species, who can easily replace the fluid lost, but it is a critical limiting factor to desert and arid habitat tortoises where water is scarce and often completely unavailable for extended periods. Blood urea levels rise and excess uric acid precipitates within the body, principally within the bladder and renal system, but other areas can be affected too as mentioned above.
The photo above shows an example of this. Some wild-caught Egyptian tortoises that were rescued from a market in a severely dehydrated condition. Following soaking in clean water, and spraying with a hose to simulate rain, they began drinking and emitted large amounts of highly granulated, coloured urates. Normal urates will. be white, in suspension, and creamy, rather than granulated, dry and coloured. The latter is a strong indicator that the animal has been subjected to an extended period of dehydration.
Many people seem to believe that Mediterranean tortoises naturally acquire almost all of their fluid requirement from their food and that therefore they do not require additional drinking water. One book on keeping Mediterranean tortoises even suggests that "only sick tortoises" voluntarily drink fresh water. It is highly regrettable that such dangerous misinformation is in circulation. This latter contention is simply not true, as direct observations of Testudo graeca and Testudo hermanni in the wild all too easily confirm.
Both species are at their most active during or just after episodes of rain, and can be observed to 'nose' along the ground, drinking from any available puddle. In Spain, France, Italy and Greece wild Testudo hermanni have been observed in some numbers to drink rainwater and to increase their activity level during wet weather, especially during summer thunderstorms, when the rain brings welcome relief from the searing heat and aridity of summer. In North Africa and Spain (T.graeca), Greece and Turkey (T. ibera), tortoises have been observed drinking from the edges of streams, from reed-beds and from puddles during episodic rain. Once, in Morocco, following the heaviest rain for many years, tortoise activity was as high as I had ever seen it and numerous individuals were observed drinking from surface water. In many arid regions, tortoise activity ceases entirely during summer or in extended periods of drought, and only resumes when rain returns. In southern Turkey, Spain and Morocco, tortoises aestivate during summer because food and water availability is so poor.
In southern Africa it is commonplace to see Stigmochelys pardalis (Leopard tortoises) drinking from streams, waterholes and pools, and Moll and Klemens also reported on the utilisation of standing water pools by Malacochersus tornieri (pancake tortoises) in Tanzania.
Mediterranean tortoises are indeed adapted to withstand a semi-arid environment. Their system of eliminating waste via uric acid rather than via urea is clear evidence of this. Uric acid can be eliminated using far lower levels of water 'wastage' than can systems based on urea, such as those of mammals and amphibians.
It is also significant that species from damp environments such as rainforests, e.g. Chelonoidis denticulata, feature a very different urinary biochemistry than do species from more arid environments such as Testudo graeca. In the former the ratio of excreted uric acid to ammonia is 6.7:6.00 and in the latter it is 51.9:4.1
Mediterranean tortoises, and most other arid habitat species, can therefore eliminate nitrogenous waste products with very great water economy. Their behaviour is also programmed to reflect this need not to waste precious water.
It was noticeable that during the rainy periods experienced in Morocco and Spain many traces of uric acid deposits were in evidence as tortoises urinated while they drank. In an arid environment it pays not to dispose of vital body fluids unless you can be sure of replacing them.
Examples of expelled urates from wild Testudo graeca graeca observed a day after heavy rain.
This is another reason why handling wild tortoises is not recommended, especially during or just before 'dry seasons'. They rely upon retained fluids for survival. Careless handling or disturbance can cause them to void this precious water.
Wild tortoises will tortoises will often drink and urinate simultaneously during episodes of rain. This behaviour can often be prompted in captivity by lightly spraying the animals with a garden sprinkler.
Just because they are able to tolerate water deprivation for a substantial period is not reason to deprive them of it deliberately or permanently. Water deprivation is a sub-optimal state which, if extended beyond certain limits, results in serious health problems. Food alone is not normally an adequate source of the total water requirement of semi-arid habitat reptiles.
We have seen several cases recently in which tortoises reared on the basis proposed, i.e. no access to fresh water and an expectation that all fluid requirements can be met entirely from food, have accumulated serious concentrations of uric acid in the bladder. This is hardly surprising and is precisely what one would expect from such a regime, given a fundamental understanding of tortoise biology and ecology. In the long term such animals can also be expected to develop kidney disease and articular gout.
In the wild, during hot and rain-free summers, aestivation or semi-aestivation occurs. There are several triggers to aestivation. Lack of food and environmental water are major factors, as is temperature. In Morocco aestivation typically begins when ambient temperatures exceed 31º-32ºC. Peak tortoise activity in the south of Morocco typically occurs in the temperature range 20º-26ºC, decreasing as temperatures rise beyond 28ºC.
During aestivation tortoises maintain themselves below ground, in burrows which exhibit a reasonably stable microclimate. In these burrows temperatures are lower than those above ground and the relative soil moisture level is higher. It is not, however, a super-humid or 'moist' microclimate as sometimes imagined. Combined with reduced (practically zero) activity, these factors result in a vastly reduced rate of fluid loss via exhalation or losses through the skin, far lower levels of generated uric acid, and little or no need to urinate.
The advice of the Tortoise Trust on this topic is very clear. Fresh water should be provided to all tortoises on a regular basis. Even true desert species such as Testudo kleinmanni, Centrochelys sulcata and Gopherus agassizii will drink given the opportunity.
For juveniles a water dish of the type shown should be made available and the water changed regularly. This will encourage drinking.
Our own exceedingly healthy breeding group of T. kleinmanni were provided with fresh water daily, and often took advantage of it. The suggestion that only sick animals drink is absolute nonsense and is unsupported by any ecological, biochemical or veterinary study we have been able to trace. There are, however, literally dozens of readily available reliable and authoritative references which support the opposite view.
What about regular soaking?
This is where it gets slightly more complex. In an outdoor environment soaking should really be an entirely voluntary thing. A shallow dish or tray in the enclosure will suffice. Be sure to keep this clean, as tortoises will often defecate in water, so this can become a vector for parasite or disease transmission. So, only leave the water there for a few hours, then clean the container thoroughly. Some species, such as Galapagos and Seychelles tortoises, or Leopard tortoises in South Africa do seem to soak in ponds, water holes or in muddy areas quite regularly. Other species, however, do so only rarely. Again, if a suitably large 'dish' or shallow tray with water is made available, they can then make that decision for themselves. For indoor tortoises, to be on the safe side, we would suggest soaking regularly, at least 2-3 times a week for at least 20 minutes to reduce the risk of bladder stones.
An alternative approach is to remove the tortoise to a 'soaking bath' type container on a regular basis. This too will encourage drinking and the elimination of accumulated urates. Never 'share' this water or container with others unless thoroughly cleaned and disinfected first.
For tortoises kept indoors, however (which comes with its own set of problems), more regular soaking may help to off-set the intense drying effects of artificial heat sources.
Precisely how effective this is, or how frequently it may be required, is difficult to quantify. There are a number of variables. We do know that artificial heat lamps will cause the local relative humidity in a basking area to plummet drastically. Here is one example that illustrates this as a halogen basking lamp is turned on and off. The black line indicates the temperature, the green line indicates the relative humidity.
Even if the rest of the indoor habitat has reasonable levels of ambient RH (typically 40-60% depending upon the species), directly in the basking zone the levels, where the tortoise typically spends a substantial amount of time, the levels can reduce to just over 20%, which could certainly be problematic. This is in addition to the direct 'drying' effects from such lamps upon the living tissues of the animal, exacerbating the problem substantially. Look for our updated report on the effects of basking lamps (coming soon). In such circumstances, it may be wise, therefore to provide regular soaking in an attempt to provide some relief from these issues. Minimising exposure to artificial light and heat sources is also recommended.
It is important to address a couple of common myths and misunderstandings
Do tortoises drink through their noses (nares)?
Tortoises do have a connection from the nares to the mouth through small openings in the roof of the mouth, called the choana. Very small quantities may enter via this route while the tortoise has it's head submerged but the vast bulk of fluid intake is, as you would expect, through the mouth. It is actually the case that more frequently water is expelled via the nares while drinking due pressure differentials. What may be confusing people is that they do not need to open their mouths very wide at all in order to drink. Only a very narrow degree of opening is required, and the mouth barely moves during this process. You can, however, see the neck 'pulse' as fluid is taken.
Can tortoises drink or hydrate via the cloaca?
There is absolutely no convincing evidence for this. Some very, very slight degree of absorption is just barely possible, but the amount involved would be absolutely minimal and insignificant. Some years ago we did a series of simple tests where we soaked two groups tortoises for 15 minutes. Some were in a container where they could not actually drink, others in a container that did permit drinking. They were weighed on precision laboratory scales accurate to fractions of a gram before and afterwards. The weight increase in the tortoises that drank was substantial and obvious. In those that did not drink no perceptible gain whatever ocurred. There is one interesting species (Chinese softshell turtle) Pelodiscus sinensis, for example, that has a rather unique nitrogenous waste metabolism that enables them to expell some urea orally, but this has never been recorded in any terrestrial species, and even in that extremely unusual case no record of cloacal fluid uptake was noted. Trials on other species have also proved consistently negative. Gibbons (2009) notes: “There is no evidence to support the hypothesis that reptiles might “drink” via the cloaca, though some authors have misreported the results of studies on the hypothesis”.
Can tortoises drink or hydrate via the skin?
No. The skin of arid habitat tortoises is highly protective. It is designed to keep precious fluids in. It is just as effective at keeping them out. Desert and arid habitat species typically also feature heavier keratinised limb scales which offer additional protection vs. the softer, less scaled skin areas of rainforest or moist habitat species, e.g., box turtles or hingeback tortoises. Amphibians, however, have a much more porous skin, that in some cases even allows gas exchange to occur (e.g, lungless salamanders). Their skin loses water far more easily than desert reptiles and requires them to inhabit moist habitats or well-protected moist microclimates.
References:
Peterson, C, and Greenshields, D. Negative test for cloacal drinking in a semi-aquatic turtle (Trachemys scripta), with comments on the function of cloacal bursae. August 2001. Journal of Experimental Zoology 290(3):247-54
Gibbons PM. (2009). Critical care nutrition and fluid therapy in reptiles. Proceedings of the 15th Annual International Veterinary Emergency & Critical Care Symposium. September 9-13. Chicago, Illinois. Pp. 91-94.
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