Silica Sand for the water filtration What do you know about filter sand and gravel At first, we need to know where the idea of using sand and gravel in filtering process came from? The idea of filtering water to obtain clean drinking water dates back to the Pharaonic Era, i.e. 4000 BC, where researchers found traces of a sand filter in Alexandria dating back to the year 50AD. This filter was used to filter water to obtain safe drinking water. Since then, the idea of using sand filters to treat surface water came to light, with the purpose of purifying such water to obtain safe drinking water. At the beginning of the application of the theory of filtering by sand and gravel, slow sand filters were designed, where they were used extensively in England and Scotland. This was followed by the expanded use of slow sand filters about fifty years later in the United States of America. In 1880, Patrick Clark developed the slow sand filter, increased the filtering rate and reduced the area of land used to construct filters in the United States of America, in particular the State of New Jersey. Developed sand filters with high filtering rates were called Rapid Sand Filters. Such filters were of great benefit in case of not using treatment by chemical clarification, which is followed by the sedimentation process. After that, several types of filters were invented, as they were classified according to filtering rates, operating methods, direction of water flow and method of controlling the sedimentation process. That's where the research started to know how to choose the filtering medium for filters, as many kinds of natural materials were used as a filtering medium, including: Silica Sand Anthracite Coal Granet Ilmenite â?»After several experiments, it was found out that the first type, i.e. silica sand, is the most commonly used type in Egypt and it was brought from sand quarries, as it was found out that silica sand is cheap compared to other types and there are large quantities in Egypt. When taking a sample of sand or gravel from any area in the quarry, we notice that it contains grains of different diameters. In order to find out the percentage of components of sand sample on the basis of diameters, we use a set of sieves placed over each other to pass a specific weight of sand and know the weights of sand with different diameters in each sieve, in order to indicate the percentage of weights of sand grains with different diameters. This process is known as (testing sand grains by sieves). We will address this topic in detail in the next article, God willing.