“Diuretics help the body get rid of excess fluid, mainly water and sodium. Most stimulate the kidneys to excrete more sodium into the urine. When diuretics flush away sodium, the body also flushes away water.”
To put it simply, diuretics are substances that make you pee more.
First of all, when you drink coffee, you also drink water. And this adds to your fluid intake.
A study published in the Journal of Human Nutrition and Dietetics reported an absence in evidence that tells us caffeinated beverages cause loss of fluid. 
Furthermore, this study published in the Public Library of Science (PLOS) reports there is “no evidence of dehydration with moderate daily coffee intake.” In fact, three cups of coffee are just like drinking three cups of water in a day. 
Essentially, any fluid leaving the body because of caffeine’s diuretic effects gets replaced with water from coffee (and other caffeinated drinks). Not only are the diuretic effects of caffeine slim, but your body also adapts to it fast.
#2: Does coffee help you sober up?
Some people think coffee can fast-track your recovery from one too many G&T’s. Or it can help you get over your terrible hangover the morning after. Coffee may help fight drowsiness caused by alcohol , but it may not take you back to sober town.
Firstly, drinking coffee to get rid of intoxication could only lead to poor decisions. A study published in the Behavioral Neuroscience reports that awareness and wakefulness brought about by caffeine can make you think you’re sober and completely capable of driving. 
Researcher Thomas Gould, Ph.D. explains to the American Psychological Association: [6, 7, 8]
The myth about coffee's sobering powers is particularly important to debunk because the co-use of caffeine and alcohol could actually lead to poor decisions with disastrous outcomes... People who feel tired and intoxicated after consuming alcohol may be more likely to acknowledge that they are drunk. Conversely, people who have consumed both alcohol and caffeine may feel awake and competent enough to handle potentially-harmful situations, such as driving while intoxicated or placing themselves in dangerous social situations.
Secondly, your body metabolizing alcohol takes time, and there’s no shortcut to it.
So keep your sloshed brain from tricking you about sobriety by sticking to drinking water and eating meals instead.
#3: Does coffee stunt your growth?
Some parents think that coffee would stunt their kids’ growth and create side effects early on in childhood. There have also been studies linking caffeine intake to decrease in bone mass and calcium absorption.
One study published in The American Journal of Clinical Nutrition, led by Douglas Kiel, MD at Harvard Medical School, reports that caffeinated soda causes lower bone mineral density among elderly women. 
Another study led by Robert Heaney, MD at the Creighton University School of Medicine, notes that most research linking caffeine to bone mass is conducted on elderly people whose diets are already low on sources of calcium because they drink so much coffee and soda and don’t drink anything else. 
These studies are not considered enough evidence to prove coffee in fact stunts growth. In fact, Harvard Health tackles the question of caffeine and stunting and says: 
Whether or not coffee turns out to have significant health benefits, this popular beverage doesn't stunt your growth. Your height is largely determined by the height of your parents and the quality of your diet and overall health while growing. If you eat a balanced diet and take measures to avoid osteoporosis, you're likely to achieve the maximum height "allowed" by your genes. And, sorry: Just as drinking coffee won't make you shorter, avoiding it won't make you any taller.
But there is another fact that strikes down the coffee stunts growth idea: Most people attain their maximum height in their late teens, well before they start drinking coffee habitually.
Years ago, some studies reported a heightened risk of osteoporosis among coffee drinkers. The studies said caffeine stimulates the body to eliminate calcium, which can be a factor in osteoporosis.
There was some alarm over this because millions of coffee drinkers could be at risk for calcium loss leading to osteoporosis. But the loss of calcium from caffeine consumption was small. Also, a link between osteoporosis and coffee was never substantiated.
Harvard Health reports:
In fact, when the studies suggesting a link were analyzed, it turned out that people who drank more coffee drank less milk and other calcium-containing beverages. So it was probably the dietary intake of calcium and vitamin D among coffee drinkers, not the coffee, that increased the risk of osteoporosis.
Harvard advises people who may have lingering uneasiness about calcium loss from coffee to take calcium and vitamin D supplements or to get them in their diets.
Erectile dysfunction. In combination, those are two of the ugliest words known to man. But can caffeine help you get it up?
Science hasn't found the definitive answer to this question, but one study concluded that fewer men who consume caffeine have problems performing. The study said:
Caffeine intake reduced the odds of prevalent ED, especially an intake equivalent to approximately 2-3 daily cups of coffee (170-375 mg/day). This reduction was also observed among overweight/obese and hypertensive, but not among diabetic men. Yet, these associations are warranted to be investigated in prospective studies