Water content

Water content or moisture content is the quantity of water contained in a material, such as soil (called soil moisture), rock, ceramics, crops, or wood. Water content is used in a wide range of scientific and technical areas, and is expressed as a ratio, which can range from 0 (completely dry) to the value of the materials' porosity at saturation. It can be given on a volumetric or mass (gravimetric) basis. Water content or moisture content is the quantity of water contained in a material, such as soil (called soil moisture), rock, ceramics, crops, or wood. Water content is used in a wide range of scientific and technical areas, and is expressed as a ratio, which can range from 0 (completely dry) to the value of the materials' porosity at saturation. It can be given on a volumetric or mass (gravimetric) basis. Volumetric water content, θ, is defined mathematically as: where V w {displaystyle V_{w}} is the volume of water and V wet = V s + V w + V a {displaystyle V_{ ext{wet}}=V_{s}+V_{w}+V_{a}} is equal to the total volume of the wet material, i.e. of the sum of the volume of solid host material (e.g., soil particles, vegetation tissue) V s {displaystyle V_{s}} , of water V w {displaystyle V_{w}} , and of air V a {displaystyle V_{a}} . Gravimetric water content is expressed by mass (weight) as follows: where m w {displaystyle m_{w}} is the mass of water and m {displaystyle m} is the mass of the substance. Normally the latter is taken before drying: except for woodworking, geotechnical and soil science applications where oven-dried material is used instead: To convert gravimetric water content to volumetric water content, multiply the gravimetric water content by the bulk specific gravity S G {displaystyle SG} of the material: In soil mechanics and petroleum engineering the water saturation or degree of saturation, S w {displaystyle S_{w}} , is defined as where ϕ = V v / V {displaystyle phi =V_{v}/V} is the porosity, in terms of the volume of void or pore space V v {displaystyle V_{v}} and the total volume of the substance V {displaystyle V} . Values of Sw can range from 0 (dry) to 1 (saturated). In reality, Sw never reaches 0 or 1 - these are idealizations for engineering use.