"Thousands have lived without love, not one without water." W. H. Auden
As Auden alluded, water is the basic stuff of life. Living creatures, like young kittens, may go for some considerable time between meals, but not between drinks. Like us, their bodies comprise mainly of water, perhaps as much as 75% water, for an 8-week old kitten. Water is the substrate in which all the chemicals of the body are dissolved, all cells are bathed, and all cell contents are suspended. It is also the essential vehicle of the circulatory system. Nothing in the body goes anywhere without water. As little as a 10%-15% reduction in total body water can result in death. And water doesn't just sit there in a static pool. It is constantly lost and replenished resulting in a dynamic status quo. On the outputside of the equation are a) urine output and b) "insensible loss" caused by from evaporation from the lungs (plus a small amount from the skin and digestive tract). On the intake side, water is imbibed in food and as free water, and some is produced by metabolism. Water output and intake must balance if things are to remain the same. If output is greater than intake, dehydration results. If intake is greater than output, overhydration results (though the latter is somewhat rare).
24-Hour Water Balance
Water Intake(20-30 ml/lb)(+ metabolism 2-3 ml/lb) = OUTPUT
OUTPUT= Urine(10-15 ml/lb) and Lungs(10-15 ml/lb)
In Charles Dickens' David Copperfield, Mr. Macawber says, with respect to money, "Income 6 pence a week, expenditure 5 pence a week, result happiness: Income 6 pence a week, expenditure 7 pence a week, result misery." The same dynamic holds true for water balance. The two sides of the equation must balance for things to remain the same and for life to proceed as usual.
In order to ensure that water intake is not compromised, clean fresh water should be available for kittens 24/7. There is never an excuse not to have water around. When a kitten is scheduled for surgery, do not withhold water from the night before even if called for by an outmoded protocol. Water should be available to the kitten until an hour or two before the procedure to avoid dehydration and increased anesthetic risk. During surgery, the veterinarian may hydrate the kitten by means of intravenous or subcutaneous fluid administration. The kitten should also be observed to make sure it resumes drinking shortly after the procedure.
The actual volume of water the kitten needs to take in, in the form of free water, depends on whether it is eating dry food or wet food. With dry food, the water intake will be at the higher end of the range indicated above. However, wet food contains 75% water (approximately) so an amount closer to the low end of the scale may be more appropriate. But don't worry about how much you kitten drinks. Internal mechanisms closely regulate kittens' water intake - unless they are sick. If problems of water consumption become apparent (too little or too much), contact your veterinarian immediately.
On the output side, a kitten's continuous production of urine means that it is being properly hydrated. One of the first things to happen when there's not enough urine around is that anti-diuretic hormone (ADH) is secreted by the pituitary gland, reducing urine production to a very low level. In one physiology textbook, it says that urine output (of people) in Baghdad is "like a puff of dust." This is because water is so scarce that Baghdadians continuously secrete large volumes of ADH to conserve their body water. Under these circumstances, the urine produced is very concentrated, and has to be to remove waste products without wasting too much precious water. Though this compensatory mechanism exists, it is better not to put it to the test with a young kitten. Anyway, insensible loss continues unabated and cannot be curtailed in the same way.
Loss of water from the lungs occurs during the process of breathing, as a result of evaporation of water from the lung lining. Evaporative cooling that occurs during this process is one of the ways kittens increase heat loss from their bodies. If a kitten becomes overheated, it will breathe more quickly, or even pant, to increase evaporative heat loss - but note, water is lost from the lungs during this process. Increased water loss in this way requires that water intake increases in compensation, if urine output is to remain uncompromised. So, if it is hot outside, it is even more important to make sure that your kitten has a constant supply of water.
From the above discussion, you will see how important water is to kittens, to their very makeup, and to the processes that ensure their viability. Shortage of water, or uncompensated, or excessive loss of water, as occurs in heat stroke and some metabolic disorders, will rapidly cause dehydration and a kitten's premature demise, if unattended. As Leonard DaVinci said, "Water is the cause, at times, of life or death," and as Benjamin Franklin is quoted, "When the well is dry, we learn the worth of water." All too true.