Water Content

The water content (w), also called natural water content or natural moisture content, is the ratio of the weight of water to the weight of the solids in a given mass of soil. This ratio is usually expressed as a percentage.

Water Content, w = Weight of water present in a given soil mass / Weight of dry soil
= (Weight of wet soil sample (W2) - Weight of dry soil (W3)) / (Weight of dry soil (W3) - Weight of container (W1))

The water of a soil sample can be determined by the following methods:

  1. Oven drying method.
  2. Pycnometer method.
  3. Sand bath method.
  4. Alcohol method.
  5. Calcium carbide method.
  6. Radiation method.
  7. Torsion balance method.

For many soils, the water content may be an extremely important index used for establishing the relationship between the way a soil behaves and its properties. The consistency of a fine-grained soil largely depends on its water content. The water content is also used in expressing the phase relationships of air, water, and solids in a given volume of soil. Soil mass is generally a three phase system. It consists of solid particles, liquid and gas. For all practical purposes, the liquid may be considered to be water (although in some cases, the water may contain some dissolved salts) and the gas as air. The phase system may be expressed in SI units either in terms of mass-volume or weight-volume relationships. The inter relationships of the different phases are important since they help to define the condition or the physical make-up of the soil.