Lateral. The smaller pipes of a filter underdrainage system which are connected to the
main pipe, or manifold, and which contain orifices through which the filtered water
Level, Hydrostatic. The level of elevation to which the top of a column of water would
rise, if afforded opportunity to do so, from an artesian aquifer, or basin, or from a
conduit under pressure.
Level, Pumping. The elevation at which water stands in a well when the well is being
pumped at a given rate.
Level, Static. The elevation of water table or pressure surface when it is not influenced
by pumping or other form of extraction from the groundwater body. It is the level of
Lime-Soda Ash Softening. A process of softening water by adding lime to precipitate
carbonate hardness and soda ash to precipitate noncarbonate hardness, with
subsequent removal of precipitate by sedimentation and filtration.
Liter. 1,000 milliliters; practically 1,000 cubic centimeters.
Main. A pipeline on the discharge side of a water pumping station.
Maintenance. The upkeep necessary for efficient operation of physical properties. It
involves labor and materials, but is not to be confused with replacement or retirement.
Man-Made Beta Particle and Photon Emitters. All radio-nuclides emitting beta particles
and/or photons listed in Maximum Permissible Body Burdens and Maximum
Permissible Concentration of Radionuclides in Air or Water for Occupational Exposure,
NBS Handbook 69, except the daughter products of Thorium-332, Uranium-235, and
Manometer. Single or double (U-tube) glass tube containing a liquid; and indicating
instrument used for measuring flow pressure or liquid level.
Maximum Contaminant Level. The maximum permissible level of a contaminant in
water which is delivered to the free flowing outlet of the ultimate user of a public water
system, except in the case of turbidity where the maximum permissible level is
measured at the point of entry to the distribution system. Contaminants added to the
water under circumstances controlled by the user, except those resulting from corrosion
of piping and plumbing caused by water quality, are excluded from this definition.
Maximum Total Trihalomethane Potential (MTP). The maximum concentration of total
trihalomethanes produced in a given water containing a disinfectant residual after 7
days at a temperature of 25C or above.