“When the well is dry, we learn the worth of water.”
Benjamin Franklin
     
  Water is a chemical substance with the chemical formula H2O. Its molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state, water vapor or steam.  
   
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Sand Filters

Sand based water filters have been used for over 100 years to treat waste water. They are generally used on a larger scale to treat a water supply for a whole community. Most units require a constant flow of water to work correctly.

Sand filters are used for water purification. There are three main types;

1. rapid (gravity) sand filters

2. upflow sand filters

3. slow sand filters

All three methods are used extensively in the water industry . The first two require the use of flocculants chemicals to work effectively whilst slow sand filters can produce very high quality water free from pathogens, taste and odor without the need for chemical aids.