Diarrhea

Nausea

Intestinal or Stomach Cramping / Aches and Pains

Dehydration

In some cases the water could smell or taste different. However, many contaminants have no taste or odor. Boiling does kill most types of parasites, bacteria, and viruses. Yet, the most effective way to ensure that the water we consume is not contaminated is  to perform water tests.

According to Professor Benjamin Sovacool from Aarhus University, Denmark,  unless water use is drastically reduced, severe water shortage will affect the entire planet by 2040.

Within three decades, almost 80% of the lands that depend on groundwater will start to reach their natural irrigation limits as the wells run dry. It is estimated that, by 2050, environmental flow limits will be reached for approximately 42% to 79% of the watershed in which there is groundwater pumping worldwide, and this will generally occur before substantial losses in groundwater storage are experienced.  
As you can see down below, we do have a lot of water on earth, but only %3 is useful to human beings and even with the desalination, it is feared that it won’t be completely enough for all the population.

4- Population increase

Inadequate sanitation is also a problem for 2.4 billion people—they are exposed to diseases, such as cholera and typhoid fever, and other water-borne illnesses. Two million people, mostly children, die each year from diarrheal diseases alone.