According to the book "Your Body's Many Cries for Water" written by F. Batmanghelidj, M.D., the following health problems are caused primarily by chronic dehydration:
Heartburn, Dyspeptic Pain, & Gastritis
When the mucus barrier around the stomach is well-hydrated, it retains bicarbonates and is better able to neutralize acids as they pass through the mucus. Also, water plays a very important role in the digestive process. Without water, complete digestion is virtually impossible.
High Blood Pressure
When your blood is dehydrated, it loses volume and becomes thicker. As a defense mechanism, the body will constrict its blood vessels to retain sufficient pressure for circulation. Keeping your body well-hydrated keeps your blood volume high and keeps your blood less viscous (thinner), keeping your blood vessels more open. It is also important to note that when your blood is dehydrated, your body will "steal" water from inside of the cells to keep the water content of the blood as high as possible. So, when you have high blood pressure or hypertension, it is also very likely that your cells are severely dehydrated… which can lead to an entire host of major health problems.
Alzheimer's and Poor Brain Function
When brain cells become chronically dehydrated, they begin to shrink, at which time many of the functions of brain cells become compromised. Dehydration of the brain also compromises the transport system that delivers neurotransmitters to nerve endings.
Constipation and Colitis Pain
One of the main functions of the large intestines is to remove water from the waste. When a person is dehydrated, however, the waste becomes too hardened which makes its passage more difficult, leading to constipation and colitis pain.
Arthritis and Joint Pain
The cartilage in joints contain a lot of water which allow for opposing surfaces to glide freely over each other during joint movement. When cartilage becomes dehydrated, however, friction causes more damage and the cartilage in not able to regenerate as quickly as it is being destroyed. This can lead to pain and joint stiffness as the cartilage deteriorates.
Back and Neck Pain
Spinal joints and discs are dependent upon the hydraulic properties of the water stored in the disc core and cartilage. Not only is water a lubricant, it actually plays a vital role in supporting spinal compression. When the disc or spinal joints are dehydrated more weight is placed on the spine (because less weight is carried by the water), which can lead to pain.
The basic cause if headaches (migraines) is the excessive dilation of the peripheral vessels in the brain. Sufficient hydration is the most efficient way of preventing this dilation.
When the body is severely dehydrated, it "steals" water from the cells. The cells then defend themselves by producing cholesterol which serves as a "clay" that makes the cell wall impervious so that no more water can be removed. This is a natural way that your cells protect themselves against dehydration.
Excessive Weight Gain
We eat primarily to supply the brain with the energy needed for its round-the-clock work. The brain gets energy from two sources: either from sugar in blood circulation, or "hydroelectricity" produced as water passes through cell membranes. When the brain needs energy, it puts out signals of either thirst or hunger. Unfortunately, most people do not recognize these signals as thirst signals, only as hunger signals. However, only about 20% of the food we eat reaches the brain. The rest goes to other parts of the body and will eventually become stored if muscle activity does not use it up. Since water moving through the cell membrane can also create energy for the brain, it is better to drink water than to eat food. Excess water does not store and create weight gain like excess food does. Therefore, drinking sufficient amounts of water helps reduce overeating.
Asthma and Allergies
Asthma and Allergies are indicators that the body has resorted to an increase in the production of the neurotransmitter histamine. Histamine is the sensor regulator of water metabolism and its distribution in the body. It has been shown in animals that an increase in water intake will reduce histamine production in histamine producing cells.