Moderate alcohol consumption does not pose a risk to healthy kidneys. In fact, studies seem to indicate that moderate drinking may actually reduce the risk of kidney cancer and chronic kidney disease.
Having said that, though, it's still wise to note that the key words in the phrase "tossing a few back" are, "a few".
Even if you are a moderate drinker, be aware that alcohol can put a strain on the kidneys in a number of ways.
Having too many drinks too often can cause the kidneys to enlarge, and can increase the risk of diseases of the liver, which can damage the kidneys in the form of kidney failure.
Imbibing too frequently and too well can increase the risk of high blood pressure, which can lead to kidney disease. It can also increase the risk of diabetes, which can lead to kidney failure.
Indulging too freely and extensively can increase the risk of albuminiria (too much protein in the urine).
The cells in the muscles may release electrolytes, which then triggers osmosis (taking water from the cells and putting it into the blood stream) to correct the electrolyte imbalance.
This drying out can have a damaging effect on cells and organs.
Alcohol consumption irritates the kidneys and affects hormone regulation of water balance in the body. The pituitary gland in the brain manufactures vasopressin, or anti-diuretic hormone (ADH).
ADH regulates the kidneys' fluid output through urination, and controls the concentration of the urine's contents. When ADH is not doing an optimal job, we lose too much water.
The kidneys control the amounts of electrolytes like chloride, magnesium, potatassium, phosphate and sodium. Alcohol consumption affects the amount of electrolytes in the bloodstream, so that the amount is too high from some types of alcohol, or too low from others.
In the case of hard liquor like vodka or whiskey, release of ADH slows down, and urine production is increased. Now the amount of electrolytes in the bloodstream is too high.
This leads to excessive fluid loss through urination and can cause dehydration.