Glossary, A to Z

A set of valves near the meter that stops water on a property from flowing back into the public main. The State Water Board's handbook requires each one to be field tested at least once a year by a certified tester. See §5.1.1, §1.1.3, §7.3.5, §1.2.6.

A quarter-turn valve with a lever handle. The lever runs along the pipe when the valve is open and straight across it when closed. See §4.4.5.

An activated-carbon filter medium that NDSU Extension describes as designed to adsorb chloramines. See §2.4.3.

The disinfectant the inland North County districts report in their water; Rainbow notes that parts of its system switch to free chlorine at times. A softener does not remove it; carbon media is the tool for that. See §2.4.1, §2.4.3, §2.4.6, §2.4.2.

The Contractors State License Board. It requires a license for work of $1,000 or more in combined labor and materials, per its consumer page. See §4.5.2, §6.4.2, §4.5.1, §4.3.3.

The cleared and managed ground around a house that slows a wildfire. San Diego County's emergency office calls 100 feet of it the law on its wildfire page. See §7.2.1.

A backflow assembly with two check valves and no relief valve. The state handbook sets a double check as the minimum for many premises with a fire protection system, though some low-hazard home systems need none; Valley Center MWD requires at least one on any service with a private well. See §5.1.2, §5.1.5, §7.3.5.

The wholesaler that Fallbrook PUD began buying from on January 1, 2024, and Rainbow Water after its detachment became final on November 1, 2024. See §2.2.1.

A small tank on the cold line that gives heated water room to expand in a closed system. The 2025 California Plumbing Code §608.2 calls for one after every pressure regulator. See §3.3.3, §3.3.1, §6.2.4, §1.1.2.

The small red dial on a meter face that turns whenever water passes through. Valley Center MWD's meters call it the "Tattle Tell". See §4.1.1, §1.2.2, §4.1.2, §4.3.2.

The hardness unit softener makers and test kits use. One grain per gallon equals 17.1 mg/L, the factor Fallbrook PUD and Rainbow print. See §2.1.1, §2.1.2, §1.1.1, §6.1.1.

Dissolved calcium and magnesium, counted as calcium carbonate. The USGS calls 0-60 mg/L soft, 61-120 moderately hard, 121-180 hard and over 180 very hard. See §2.3.2, §2.1.6, §2.1.1, §6.1.1.

An outdoor faucet with a hose thread, the place to screw on a pressure gauge. See §3.1.1, §3.1.2.

The water districts' name for the main shutoff on the supply pipe between the meter and the house. See §4.1.3, §4.3.2, §4.4.2, §1.2.3.

A spring-loaded regulator on the owner's side of the meter that lowers street pressure to a steady level. Code requires one where static pressure tops 80 psi. Also called a regulator or PRV. See §3.2.1, §3.2.4, §4.4.2, §3.4.3.

Pounds per square inch, the unit on a water pressure gauge. See §3.1.3, §3.1.4, §3.4.3, §3.1.5.

A backflow assembly with two check valves that work independently and a relief valve between them that opens to dump water if pressure goes wrong. Also called an RP. See §5.1.5.

The hard mineral crust that very hard water leaves wherever it is heated or evaporates: in water heater tanks, on aerators and showerheads, and on glass shower doors. See §6.1.6, §1.1.5, §2.1.5, §4.2.4.

A metal strap that ties a water heater to the wall studs. California's Health and Safety Code §19211 requires every residential heater to be braced, anchored or strapped. See §1.2.5, §6.3.5, §6.4.4.

A break in a water pipe beneath a concrete floor, most reliably detected by a meter that keeps moving while every fixture is off. See §4.3.1, §4.3.6.

Water pressure measured with nothing flowing, the figure the plumbing code's 80 psi limit refers to. See §1.1.2, §3.1.3.

The valve near the top of a water heater that opens to release water if the temperature or pressure inside gets too high. Owners operate it only as the heater's manual allows, and replacing it is licensed work. Also called a T&P valve. If you're unsure, call a licensed plumber. See §6.2.2, §1.2.5, §3.3.6, §3.1.4.

The growth in volume of water as it heats. In a closed system it raises pressure, which an expansion tank absorbs. See §3.3.1, §6.2.4, §3.4.3.

The yearly report each district publishes on the water it delivered, with hardness, sodium and disinfectant figures. Also called a consumer confidence report. See §2.1.1, §2.2.4, §4.2.3, §2.2.1.

A tank of ion-exchange resin that swaps hardness minerals for sodium. NDSU Extension says it adds about 8 mg/L of sodium for each grain removed. See §2.3.4, §2.3.6, §2.3.2, §2.4.4.

A sprinkler timer that adjusts watering from weather data. Valley Center MWD's rebate page lists up to $200 on lots under one acre, and the SoCal Water$mart residential page lists controller rebates too; confirm the current amount before buying. See §5.2.4, §5.4.5.

The first 5 feet around a house in California's defensible space bands. The Board of Forestry is phasing it in, and its rules were not confirmed final when this handbook was checked. See §7.2.1, §7.2.4.