The Water Cycle and Wells In thinking about water and the treatment of water the best starting point is with the hydrological cycle. The hydrological cycle is a combination of processes that continually recycles the water here on earth. The processes include precipitation, run-off, evaporation, transpiration, percolation and storage. Approximately 70% of the water that precipitates from the sky evaporates directly into the atmosphere, leaving the remaining 30% to run of into streams, lakes and rivers or to percolate into the ground. The water that percolates into the ground either gets used by plants, or makes its way into the soil and rocks below ground, where it is stored until it seeps back into the streams, lakes and oceans. The replenishing of the water in the ground is called recharge. All of the water is eventually put back into the atmosphere by either the transpiration from plants or evaporation from the various bodies of water. It is interesting to note that very little of this water is made available in the ground for us to extract for drinking. As a matter of fact, only about 1% of the water on the earth is available for our use. The rest is in the oceans (97%) or in the polar ice caps (2%). The water that percolates into the ground and reaches the saturated pores of the soil or fractured bedrock is called ground water. The area in which this water is stored is called an aquifer if it will allow water to be pumped from it. Aquifers are formations that have both high porosity and permeability. Porosity is defined as the percentage of pore space in the ground where the water is stored, and permeability is the measure of the capacity for flow through the porous material. Solid bedrock, such as granite, becomes an aquifer, not because the rock itself is porous, but because there are fissures in the rock that create areas of storage. If these fissures are large enough, they will allow the water to move, making the formation both porous and permeable. In the case of gravel or sand, the water actually sits between the individual grains of material. If the grains are not too fine, the gravel or sand will also be permeable. Many people think that we draw our water from underground lakes or streams. This is, for the most part, not true. The only place that one would find an underground stream flowing is in an area of limestone caves. Most of the time, the movement of water in the aquifer would not be perceptible, unless the water is pumped or viewed over very long periods of time. Wells are used to extract water from the aquifer. In general, wells can be thought of as falling into three categories. These categories are dug wells, driven points and drilled wells. A dug well is one that is either excavated by hand or dug with a backhoe. Because dug wells are generally shallow (10 ft. to 20 ft.), the water is usually a combination of surface water and ground water. A very shallow dug well of only a few feet, that has ground water bubble into it, is called a spring. Driven points are pipes that have one end sealed off in the shape of a point. The walls of the pipe have holes that are covered with screens. The point is driven into the ground and is then connected to a pump that pulls the water through the screens covering the holes in the pipe. Points, like dug wells are generally shallow and usually produce a combination of ground and surface water. Drilled wells are formed by boring a hole into the ground. These wells are generally a few hundred feet deep, although they have been drilled to over 1000 ft. Because the water we extract from the ground has dissolved minerals, gasses and biological matter, it is not always safe to drink. We test for these contaminants, and, based on predetermined guide lines called maximum contamination levels (MCL's) set by the EPA, we determine the safety and potability of the water. If the contaminants exceed these MCL's, we treat the water. Treatment can include anything from a simple cartridge filter to a combination of filters, softeners, reverse osmosis systems (RO's) and aeration systems.   Home | Top of page | Contact © Copyright 2000, Air & Water Quality, Inc. Maine's Water Experts