How much water we should drink per day ?
Each person has a need to consume different water. although the recommended guidelines for drinking water are eight glasses a day but it is so against some people this factor is able to shorten the depreciation of kidney function. Kidneys are one of the body's vital bureaus, such as heart, lung, liver and others. The function is very complex, especially as the innate washing of artificial toxins of the body's metabolism by selecting filtration tricks and removing them through the urine.

When we drink eight glasses a day, then the urine out of taste-taste as much as 1-1.5 liters. together with the evaporation of our bodies, may be with the tropic temperature of 700-800, we normally need 6-7 glasses of water per day so the rule is not legal and drink alone is comparable if the activity is more than certainly you have to drink more.

Because the body is psychologically arranged in such a way as to produce thirst. although when excessive drinking there will be consequences that create the burden of filtration for the kidneys. So far there is no data about the state of the water interest for fresh people but the water intake in certain cases should be limited. chapters show another range of ADH autonomic hormone increases in SIADH (Syndrome of Inappropriate ADH Secretion), chronic kidney disease, cardiac success and low serum albumin quality.

Excess water intake continues not recommended for old age. For research conducted Siregar et al, water intake more sourced 1,500 ml / 24 hours potentially leads to hyponatremia in old age, capable of causing awareness, convulsions and even dead.

Source: https://www.healthline.com/nutrition/8-glasses-of-water-per-day#section2
About 60-70% of our body consists of water, so the presence of water greatly affects every system in the body. Various important water roles are to remove toxins from the body's vital organs, can help bring nutrients to the body's cells, can provide moist conditions for the ears, nose, and throat, can facilitate blood flow, regulate body temperature, facilitate digestion , can lubricate and protect joint and muscle movements, and can help to restore the condition after illness.

Because of the various roles that are so important, then someone is strongly recommended to consume water in sufficient quantities every day. Good water consumption is of course water. Other types of drinks that like to consume milk, juice, tea, coffee, and soda does contain a lot of water in it. However, these types of drinks are not a major part of the total daily fluid intake of a person because they can only contribute little to the water requirement in the body. Water is still the best liquid because the water is free of calories. Another water source that can contribute to fluid needs in the body is water that comes from food. The average food can contribute about 20% of the total fluid intake. These foods are usually fruits and vegetables.

Water Requirement Per Day

Water plays an important role to expedite all existing systems in the body so that their needs must also be fulfilled. You need to know that every day someone will lose water through the movement of breath, sweat, urine, and intestinal activity in the stomach. Thus, a person must replace the condition of water loss by consuming water and water-containing foods.
I think that if you drink the recommended 8 glasses each containing 12 oz a day then you are doing really good. That is the equivalent to about 3/4 of a gallon. I would say most people don't even come close to drinking that much but you would probably be much healthier if you did. I know personal I don't enjoy drinking water at all and tend to drink a lot of sugary beverages which is not good for me at all.
Women are advised to drink 2 liters of water per day. While men need 3 liters of drinking water per day or the equivalent of 15 glasses of drinking water.

"But some of the water you drink does not always come from a drink, and a lot of water is calculated to meet your daily fluid needs so you do not have to drink as much water as you think," he explained.

"In essence listen to your body, your body can send a signal clearly whether you drink a lot of water or even lack of water, so pay attention to every signal issued by the body for the health of the body."
Most people have the opinion that we should drink at least 2liters of water a day.
Well that is wrong.
You should consume 2liters of liquid a day. That does include all the liquid you consume when eating a Apple for example.
As per scientific facts. There are many different opinions on how much water you should be drinking every day. Health authorities commonly recommend eight 8-ounce glasses, which equals about 2 liters, or half a gallon. This is called the 8×8 rule and is very easy to remember.
you should alteast drink 4 litres a day to get himself hydrated
2-4 Liters.
If you doing hard work you should drink huge glasses of water like 3,4 liters.
Water is essential for human survival. An adult body is made up of about 60 percent water, and a newborn is made up of 74 percent of water. Water removes waste from cells, brings nutrients to cells, regulates body temperature and helps you digest food. When you don’t consume enough water, serious complications can arise. Your hydration needs depend on exercise, diet, age, body fat, altitude, pregnancy, medications and the weather.
Here is how to calculate, how much water you should drink a day for both health and weight loss benefits.
Your weight: The first step to knowing how much water to drink everyday is to know your weight. The amount of water a person should drink varies on their weight, which makes sense because the more someone weighs the more water they need to drink. A two hundred pound man and 100 pound woman require different amounts of water every day.
Multiply by 2/3: Next you want to multiple your weight by 2/3 (or 67%) to determine how much water to drink daily. For example, if you weighed 175 pounds you would multiple that by 2/3 and learn you should be drinking about 117 ounces of water every day.
Activity Level: Finally you will want to adjust that number based on how often you work out, since you are expelling water when you sweat. You should add 12 ounces of water to your daily total for every 30 minutes that you work out. So if you work out for 45 minutes daily, you would add 18 ounces of water to your daily intake.
To make it a littler easier to calculate how much water to drink everyday, here are the recommended amounts for a range of weights. Remember to adjust for your activity level.
Weight Ounces of Water Daily
100 pounds 67 ounces
110 pounds 74 ounces
120 pounds 80 ounces
130 pounds 87 ounces
140 pounds 94 ounces
150 pounds 100 ounces
160 pounds 107 ounces
170 pounds 114 ounces
180 pounds 121 ounces
190 pounds 127 ounces
200 pounds 134 ounces
210 pounds 141 ounces
220 pounds 148 ounces
230 pounds 154 ounces
240 pounds 161 ounces
250 pounds 168 ounces
Water composition in baby's body (80%), adults (70%), and elderly (50%) vary. The organs in the body was almost composed mostly of water element. Lung (90%), blood (82%), skin (80%), muscle (75%), brain (70%), and bone (20%). So, the role of water is so great in human life to survive. But most of us have not understood the importance of water consumption for the body.

Talking about water needs for the body, there are several internal and external factors of each individual that affect it. Internal factors such as gender, age, health condition of the body, weight, habit / lifestyle. External factors that can affect individual water requirements are temperature, humidity, and individual physical activity.

In general, men will have more water needs than women. Children's water needs will be less than adults. While elderly (> 60 years) simply consume 1 - 1.5 Liter / day. Adults need about 2 - 3 Liters of water per day. The need for water in pregnant and lactating women has its own portion.