InterNACHI Pool & Spa Inspector key terms

A device at the waterline that draws surface water and floating debris into a collection basket before the water reaches the pump. It usually sits in a throat opening in the pool wall or deck.

The floating flap inside a skimmer throat that pivots with water flow to skim the surface layer and keep captured debris from drifting back into the pool.

A secondary opening below the skimmer that draws water directly from the pool if the skimmer throat is blocked or the water level drops. It protects the pump from running dry.

A submerged outlet, usually at the deepest point, that returns water to the pump and filtration system. Modern covers are designed to prevent body or limb entrapment.

A fitting that delivers filtered, treated water back into the pool. Its direction and flow affect circulation and can be adjusted to improve surface movement and chemical distribution.

The time required to circulate the full volume of pool water through the filtration system once. It is used to judge whether pump run time and flow are adequate for water clarity.

The volume of water moving through a system per unit of time, commonly expressed in gallons per minute. It must match filter and pipe capacity to avoid damage or poor filtration.

An instrument mounted on the filter that shows internal pressure. A rise above the clean baseline indicates loading and signals that backwashing or cleaning is due.

The process of reversing water flow through a filter to flush trapped debris to waste. It restores flow and is followed by rinsing before normal operation resumes.

A selector valve on a sand or diatomaceous earth filter that routes water for filtering, backwashing, rinsing, waste, recirculation, or closed service positions.

A filter that passes water through a pleated fabric element, capturing debris in the media. It is cleaned by rinsing or soaking rather than by backwashing.

A filter that uses a layer of fossilized microscopic shells on a grid to strain very fine particles. It requires periodic backwashing and replenishment of the powder media.

A removable basket at the pump intake that catches leaves and large debris before they reach the impeller. Inspectors check it for cracks, debris, and a proper lid seal.

Noise and loss of performance caused by air or vapor forming in the pump. Common causes include a clogged intake, low water level, or a leaking suction line.

A trapped pocket of air that prevents water from reaching the pump or flowing through a line. It can stop circulation after draining, winterizing, or a suction leak.

A hazardous condition in which a person is held against an outlet by suction or caught by hair, clothing, or a limb. Covers, dual drains, and safety vacuum release devices reduce the risk.

A dome-shaped or slotted grate secured over a suction outlet to spread suction over a large area and block body or hair contact. Missing or broken covers are a serious safety defect.

A device that senses a blockage in a suction line and quickly breaks the vacuum, releasing a trapped person. It must be tested and maintained to remain effective.

The active, uncombined chlorine in water that sanitizes and oxidizes contaminants. Test kits measure it separately from total chlorine to reveal how much is available for disinfection.

Chlorine that has reacted with nitrogen or organic waste and lost most of its sanitizing power. High levels produce odor and irritation and indicate a need to shock the pool.

The sum of free chlorine and combined chlorine in the water. Subtracting free from total gives the combined amount, a key indicator of water quality.

Also called stabilizer, it slows the breakdown of chlorine by sunlight. Too much reduces chlorine effectiveness, so it is tested and managed alongside free chlorine.

A scale from 0 to 14 describing how acidic or basic water is. Pool water is normally kept near neutral because extremes reduce sanitizer effectiveness and damage surfaces or equipment.

A measure of dissolved alkaline substances that buffer water against rapid pH changes. Low readings allow pH bounce, while high readings make pH hard to adjust.

The concentration of dissolved calcium in water. Low levels make water corrosive to plaster and metal, while high levels encourage scale on surfaces and equipment.

A calculated value combining pH, temperature, calcium hardness, total alkalinity, and dissolved solids to predict whether water will scale or corrode. A near-zero result indicates balanced water.

Adding a large dose of oxidizer to break down combined chlorine and organic contaminants. It is done when combined chlorine is high or after heavy bather use.

An alternative sanitizer often used in spas because it remains effective at higher temperatures and forms fewer irritating byproducts. It is tested and dosed differently from chlorine.

A valved pipe arrangement that lets water circulate without passing through the heater. It allows service or isolation of the heater and can protect it from excessive flow.

The permanent connection of all metal parts and conductive components to a common point to equalize electrical potential. It differs from grounding and is essential near pool water.

A conductive path to earth that carries fault current and helps clear a fault. It is a separate requirement from bonding and both are checked in electrical inspections.

A network of conductors around and beneath a pool that ties together metal components and the water. It limits voltage differences that could cause shock.

A protective device that shuts off power when it detects a small current imbalance, reducing shock risk. It is required for many pool and spa circuits and should be tested.

A fence, wall, or other enclosure that limits unsupervised access to a pool or spa. Inspectors check height, gaps, gates, and self-closing or self-latching hardware.

A gate that closes and latches on its own, preventing it from being left open. The latch must be positioned where a young child cannot easily reach it.

A device that sounds when a person or object enters the water or crosses the barrier. It supplements but does not replace a proper fence or safety cover.

A reinforced cover anchored around the pool that supports weight and prevents a person from falling into the water. It must be properly installed and free of tears.

An adjustable spa fitting that mixes air with water to produce a massaging stream. Inspectors check that jets are intact, functional, and not leaking.

A unit that forces air into spa jets or an air channel to create bubbles and massage action. It must have a check valve or loop to prevent water from reaching the motor.

A one-way valve that allows flow in a single direction. It is used on spa blowers, heater bypasses, and chemical feed lines to prevent backflow or water damage.

The chemical agent maintained in spa water to control pathogens. Because spas are small, warm, and heavily used, sanitizer levels must be tested and held within range.

A vessel that absorbs pressure changes in a closed loop, such as a heater system or spa plumbing. A failed tank can cause relief valve discharge or pressure swings.

A safety device that opens to release excess pressure from a heater or vessel. It must be unobstructed and piped to a safe discharge point.