Glossary of Irrigation Terms

The name given to pollution which can’t be traced to a single clear source, such as a waste-water pipe. Non-point source pollution is generally caused by rainfall or snowmelt moving through and over the ground, picking up and carrying pollutants such as fertilizers, pesticides, bacteria, sediment and other forms of man-made pollution. The pollutants are then introduced to water sources such as rivers, lakes, ground water, wetlands and the sea.

The hole in a sprinkler or emitter through which water is passed into the atmosphere. The size, shape and positioning of the nozzles in an irrigation system can have a clear impact on factors such as the distance over which water is applied, the placement of the water and the efficient distribution of irrigation in general.

A measure of the pressure at which an irrigation system actually operates. Calculated by taking the static pressure of the water at the point of connection to the water source and subtracting any pressure losses occurring through the system. The operating pressure is usually measured at the base or nozzle of the sprinklers.

An outlet valve fitted to the interior of a vertical pipe (sometimes known as a riser). The orchard valve features an opening the same size as the diameter of the pipe and an adjustable cover to enable the flow of water through the pipe to be varied. Orchard valves are similar to alfalfa valves, but deliver lower flow capacity.

Pressure, sometimes called potential, is a measure of the pressure caused by water as it moves through an irrigation system. Osmotic pressure is specifically the pressure of water which contains dissolved molecules, generally salts and other nutrients. Often the water will be passing through a semi-permeable membrane, from a less to a more concentrated solution of nutrients.   

A graph which is unique to a particular water pump. Points plotted on the curve demonstrate the capacity the pump will be capable of delivering across a range of different metrics, including the total dynamic head (TDH), which represents the water pressure and the gallons per minute (GPM), which reflects the flow rate. The performance curve can be used to find out whether a pump is suitable for a specific system.

A measure of the speed at which water applied to an area through irrigation will move through the soil, based on factors like density and texture. If irrigation is applied at a rate which is faster than the soil is able to absorb it, then water will be wasted, resulting in pooling, run off and soil erosion. Knowing the permeability of a specific area is key to delivering tailored irrigation.

A chemical agent introduced to a landscape in order to control or eliminate particular organisms. Pesticides might take the form of herbicides, fungicides or insecticides. If an irrigation system delivers water at a rate faster than the soil is able to absorb it, any pesticides present my contaminate ground and surface water.

A measure of the acidity or alkalinity of water, in particular of a water source for an irrigation system. The pH scale runs from 0 to 14, with a lower number meaning more acid in the water and a higher number more alkaline. A pH number of 7 means the water is neutral and completely pure, while high alkaline water is often called ‘basic water’.

In meteorology, precipitation is what happens when water from the atmosphere falls from the clouds, to the surface of the earth. This can be in the form of a liquid or solid state - from rain, snow, and sleet to hail. The small drops of condensed water that form clouds are too small to fall to the earth but when certain conditions prevail, they fall as precipitation. You might be interested to know that one-inch of rain falling over an area of one acre of land results in a colossal 27,154 gallons of water! (Our thanks to the US Geological Survey for that piece of information).

A pump converts mechanical energy into hydraulic energy. In irrigation terms, water pressure and/or flow is created or increased.

PVC is polyvinyl chloride, a thermoplastic polymer, it is one of the most widely used plastics worldwide. It's durable and long-lasting, very dense with excellent tensile strength. It is suitable for irrigation piping in smaller projects where less flexibility is required (for example in bends) and where there is less danger of fluctuations in pressure and movement around the pipe in-situ.

A sprinkler head is a device connected to an irrigation system and is responsible for distributing water under pressure through the air to the ground surface. Sprinkler heads come in a variety of shapes and sizes and deliver water in different types of spray patterns and water droplet sizes. Common types of head include rotary, spray, and drip heads. Because of the task they perform, they need to be able to withstand exposure to water, sunlight, and other environmental factors and are typically made of durable materials like plastic, brass, and stainless steel.

Submersible motors are designed to run when completely submerged. In an irrigation application, the submersible motor can drive a turbine pump while completely submerged. The submersible motor is purpose-designed to be robust and corrosion-resistant; water is kept away from the motor by incorporating special features such as precision-machining, hermetic seals and barriers.

Interchangeably known as electric submersible pumps, these are common in applications such as drainage, sewage and irrigation where the pump must be completely submerged in water. The motor that runs the pump (see submersible motor) is also specially designed to remain water-tight while the whole assembly is under water.