Delta in well irrigation is total depth of water required to mature a crop in meters or centimetres. The delta of well water is about 66% of canal water because conveyance losses are minimum and well water is used at right time in right quantity.

Specific capacity is rate of flow from a well per unit of a drawdown. The value is not same for all drawdowns, it should be determined for fall of first meter.

Zone of aeration is space above water table and below surface and water exists in this zone by molecular attraction. The water in this zone is not at hydrostatic pressure and gravity water moves through this zone.

A normal tubewell lasts for about 15 to 20 years in Norrn India. It may fail due to incrustation and corrosion.

Denkli is generally provided on unlined wells which are supposed to irrigate only small fields. Churus is suitable for lined wells and can be conveniently used deep wells up to a maximum depth of 30 m. Persian wheel (also known as Rahat in some parts of India) is suitable when depth of well is 12-30 m. The windmill is not very reliable.

Depending upon number of interstices present, aeration zone is divided into three classes. The capillary fringe is a continuation of zone of saturation and does contain some interstitial water. Soil zone is depth from surface penetrated by roots of vegetation and remaining intermediate part is intermediate zone.

Effective diameter is an index of measure of fineness of an aquifer. It is used for designing various intake components of a tubewell. For permeability D₁₀ (i.e. 90% grains retained on sieve) is taken as effective size.

Infiltration is process by which water seeps into surface strata of earth to meet soil moisture deficiencies. Percolation is deep vertical movement of water in ground.

Specific capacity is given by ?
Specific capacity = discharge of well / Drawdown = Q / (C₁Q + C₂Q²) = m³/sec/m = m²/sec. This equation also shows that specific capacity of well is not constant but decreases as discharge increases.

Yield of a well is rate at which water percolates into well under safe maximum depression head or critical depression head. It depends on position of water table, permeability, and porosity of soil, rate of water withdrawal from well, and amount of water storage in well.