A ladder for deck access from outside the pool, spa or hot tub.
LADDER, DOUBLE ACCESS
A ladder that straddles the pool wall of an aboveground pool and provides pool ingress and egress.
LADDER, LIMITED ACCESS
Any ladder with provision for making entry inaccessible when a pool, spa or hot tube is not in use (i.e., swingup, slide-up or equivalent).
LAMINAR
Non-turbulent fluid flow. Associated with fluid dynamics and designs of fluid tubing and pipelines.
LANGELIER SATURATION INDEX
A calculated number used to predict the calcium carbonate (CaCO3) stability of a water; whether a water will precipitate, dissolve, or be in equilibrium with, calcium carbonate. It is sometimes erroneously assumed that any water that tends to dissolve calcium carbonate is automatically corrosive. Langelier saturation index = pH - pH, where pH = actual pH of the water, and pH, = pH at which the water having the same alkalinity and calcium content is just saturated with calcium carbonate.
LIGNIN
A polysaccharide found in the cell walls of plants; a breakdown product of decaying vegetation, which may be present in surface water supplies.
LINER
That membrane that acts as a container for the water.
LINER, EXPANDABLE
A liner that is constructed of a material that has the capability of stretching into a greater depth of irregular shape other than the original construction dimensions.
LINER, HOOPER
The liner that is used to obtain greater depth by geometrical pattern construction on the liner bottom or floor to fit a predetermined size and shape.
LOWER DISTRIBUTION SYSTEM (UNDERDRAIN)
Those devices used in the bottom of a permanent medium filter to collect the water during the filtering and to distribute the water during the backwashing.