How did the word "water" open new horizons for Helen?

Helen Keller became both deaf and blind when she was nineteen months old, and she was not able to understand the world around her because of these disabilities. Her parents hired a teacher, Anne Sullivan, to help Helen learn to understand the world and communicate with others.
Anne began teaching Helen letters and words by spelling them into her palm, and though Helen was able to memorize words, she was not able to make the connection that these words all had meaning in the outside world.
It was when Anne took Helen to a water pump that Helen first had a breakthrough: the words she was learning from Anne were real things in the world around her. Anne put one of Helen's hands under the water and in the other spelled the word "water" over and over again.
Helen finally understood that all the words that Anne was teaching her were things out in the world. Helen later wrote in her autobiography,

"I knew then that 'w-a-t-e-r' meant the wonderful cool something that was flowing over my hand. That living word awakened my soul, gave it light, hope, joy, set it free! There were barriers still, it is true, but barriers that could in time be swept away."

Water was the first word that Helen Keller was able to connect to the world; it created a foundation for the understanding that she continued to develop.