Glossary/water dictionary

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oceanic

(Climate) The climate characteristic of land lares near oceans that contribute to the humidity, and at the same time have a moderating influence on temperature and the range of temperature variation. ^

open channel drainage

Drainage accomplished by open channels or ditches.^

operation and maintenance (O&M)

Operation' is the organised procedure for causing a piece of equipment, a treatment plant or other facility or system to perform its intended function, but not including the initial building or installation of the unit. 'Maintenance' is the organised procedure for keeping the equipment, plant, facility or system in such condition that it is able to perform its intended function continually and reliably.^

organic matter

Plant and animal residues, or substances made by living organisms. All are based upon carbon compounds.^

orographic precipitation

Precipitation resulting from the lifting of moist air over an orographic barrier, e.g. a mountain range.^

osmosis

The movement of water molecules through a thin membrane. The osmosis process occurs in our bodies and is also one method of desalinating saline water.^

outfall

The place where a sewer, drain or stream discharges; the outlet or structure through which reclaimed water or treated effluent is finally discharged to a receiving water body.^

overall efficiency

The ratio or percentage of the irrigation water consumed by crops to the water diverted from the source of supply (measured at the source of supply).^

oxygen demand

The need for molecular oxygen to meet the needs of biological and chemical processes in water. Even though very little oxygen will dissolve in water, it is extremely important in biological and chemical processes.^