jar test A laboratory procedure that simulates a water treatment plant's coagulation/flocculation units with differing chemical doses and also energy of rapid mix, energy of slow mix, and settling time. The purpose of this procedure is to estimate the minimum or ideal coagulant dose required to achieve certain water quality goals. Samples of water to be treated are commonly placed in six jars. Various amounts of chemicals are added to each jar, stirred, and the settling of solids observed. The dose of chemicals that provides satisfactory settling removal of turbidity and/or color is the dose used to treat the water being taken into the plant at that time. When evaluating the results of a jar test, the operator should also consider the floc quality in the flocculation area and the floc loading on the filter.

Java Programming language developed by Sun Microsystems that creates code for interactive applications that is executable on web pages by web browsers. These Java applications can execute on any platform--Mac, PC, etc.

jet stream Relatively strong winds concentrated within a narrow current in the atmosphere.

jetty A structure (e.g.; a pier, or mole of wood or stone) extending into a sea, lake, or river to influence the current or tide or to protect a harbor. On open seacoasts, a structure extending into a bay of way, designed to prevent shoaling of a channel by littoral materials and to direct and confine the stream or tidal flow. Jetties are built at the mouth of a river or tidal inlet to help deepen and stabilize a channel.

jogging Operating at moderate speed or the frequent starting and stopping of an electric motor.

joint application design (JAD) The development of system design criteria through facilitated workgroups involving systems analysts, business process functional experts, and end users of the system.

joint use storage (reservoir) Reservoir storage space that is used for more than one purpose.

joule A measure of energy, work or quantity of heat. One joule is the work done when the point of application of a force of one newton is displaced a distance of one meter in the direction of force.

JPEG (Joint Picture Expert Group). Standard for the compression of still pictures, such as those that might be used on a Web site.

judicial district Physical parameters, set by Congress, designating the counties under the jurisdiction of a United States district court.

Julian calendar A calendar introduced by Julius Caesar in the year 45 B.C., and slightly modified a few years later. This calendar provided that the common year should consist of 365 days and that every fourth year, now known as a bissextile or leap year, should contain 366 days, making the average length of the year 365.25 days. It differs from the modern or Gregorian calendar in having every fourth year a leap year, while in the modern calendar century years not divisible by 400 are common years. See Gregorian calendar.

Julian date Technique for the identification of successive days of the year when monthly notation is not desired. This is especially applicable in computer data processing and acquisition where library indexing is necessary.

juvenile water Water formed chemically within the earth and brought to the surface in intrusive rock.