Water is said to be turbid when particles suspended in it restrict the transmission of light and give a cloudy or muddy appearance. Only small particles can remain suspended for significant periods of time. Relatively large and dense particles such as sand grains will sink rapidly. All particles denser than water will tend to sink unless there is a force operating to keep them suspended. Normally some level of motion of the water assist in suspending particles. Thus the duration of suspension depends on the intensity of the motion plus the size shape and density of the particles. Soil particles and organic fragments are probably the most common materials suspended in farm water supplies.