Water Intake

A water intake is the opening through which a swim jet draws water from the swimming pool into its propulsion system. Water passes through an intake grille, moves through a pump or propeller assembly, and is discharged back into the pool to create a continuous swimming current.

As the entry point of the hydraulic circuit, the intake influences water flow, hydraulic efficiency and operating safety. Its design is particularly important in counter-current systems that circulate large volumes of water.

What Is a Water Intake in a Swim Jet?

A swim jet water intake supplies existing pool water to the equipment's propulsion mechanism. Unlike the discharge outlet, which directs accelerated water into the swimming area, the intake allows surrounding water to enter the system.

Three related terms describe different aspects of this assembly:

• Water Intake: The opening or assembly through which pool water enters the swim jet.

• Suction Inlet: An intake where water is drawn towards a pump or propulsion mechanism by a pressure difference.

• Intake Grille: A protective barrier that restricts access to internal components and prevents larger debris from entering.

Most swim jet systems recirculate water directly from the existing pool rather than using an external water supply. Unlike conventional pool filtration systems, their primary purpose is to move water to generate a swimming current, not to remove contaminants.

How Does a Swim Jet Water Intake Work?

Water moves through a swim jet in a continuous hydraulic circuit:

Pool Water → Intake Grille → Pump / Propeller → Discharge Outlet → Pool

The process involves three main stages:

1. Water Entry: Pool water passes through the intake grille, which provides a protective barrier while allowing water to reach the propulsion mechanism.

2. Water Propulsion: A rotating propeller or pump impeller moves water through the hydraulic circuit. Some systems incorporate flow-straightening components to improve discharge uniformity.

3. Water Discharge: Water exits through the discharge outlet, producing the current used for stationary swimming.

Integrated Propeller vs. Pump-Driven Intakes

The intake arrangement varies between swim jet technologies.

Integrated propeller swim jets generally house the intake grille and propulsion mechanism within the same submerged unit. This creates a relatively short internal water path without extensive external suction pipework.

Pump-driven counter-current systems may use separate suction openings connected to a pump through PVC pipework. Their performance depends partly on pipe dimensions, fittings and suction-side hydraulic losses.

Neither arrangement is inherently safer based solely on its propulsion type. Intake performance and entrapment risks depend on the specific flow rate, opening geometry, pressure conditions and protective design.

How Does Water Intake Design Affect Performance?

Three hydraulic factors influence the performance of a swim jet intake: effective open area, hydraulic resistance and positioning.

Intake Area and Water Velocity

The effective open area of an intake grille affects the average velocity of water passing through its openings.

This relationship is expressed by the continuity equation:

v = Q / A

Where:

• v = Average intake water velocity (m/s)

• Q = Volumetric flow rate (m³/s)

• A = Effective open intake area (m²)

For example, consider a swim jet moving 3,000 L/min (0.05 m³/s) through an effective grille opening area of 0.10 m².

The average intake velocity is:

v = 0.05 / 0.10 = 0.5 m/s

If the effective open area increases to 0.20 m² while the flow rate remains unchanged, the average velocity decreases to 0.25 m/s.

A larger effective open area can therefore reduce average intake velocity for a given flow rate. However, actual velocity distribution may be uneven, and this simplified calculation cannot establish whether an intake meets safety requirements.

Hydraulic Resistance and Cavitation

Water encounters resistance when passing through intake grilles, internal passages and suction pipework.

Leaves, accumulated debris, narrow openings or restrictive pipe fittings can increase hydraulic losses, potentially reducing the amount of water reaching the propulsion mechanism.

Severe inlet restrictions may also contribute to cavitation in susceptible pump-driven systems when local pressure falls sufficiently. Cavitation involves the formation and collapse of vapour bubbles and may cause noise, vibration and damage to hydraulic components.

The likelihood depends on the equipment design, operating conditions and available inlet pressure.

Intake Positioning and Air Entrainment

The location of the intake affects how water enters the equipment.

Insufficient clearance from pool walls, steps or other obstructions can restrict the approach flow. An intake positioned too close to the water surface may also draw air into the system, sometimes through a surface vortex.

This process, known as air entrainment, can cause bubbles, irregular water movement and unstable operation.

The required submergence depth and surrounding clearance depend on the manufacturer's specifications rather than a universal installation measurement.

Water Intake Safety and Australian Standards

Swim jet intakes must be designed to minimise the risk of suction entrapment, which occurs when a swimmer's hair, body or limbs become trapped at or within an intake opening.

Hair may become entangled in an intake fitting, while a body or limb can potentially block a suction opening and become held against it by pressure differences.

Protective intake grilles help reduce these hazards by restricting access to internal components and distributing water entry across multiple openings. Their effectiveness depends on the complete design, including grille geometry, fastening strength and hydraulic conditions.

Australian Standard AS 1926.3

In Australia, AS 1926.3-2010 (R2016), Swimming pool safety – Water recirculation systems, establishes requirements for skimmer boxes and other permanent water outlets in swimming pools and spas.

Its stated scope concerns permanent pool circulation openings. These provisions should not automatically be assumed to apply in full to every portable swim jet with a self-contained intake. Applicable safety requirements depend on the equipment and installation.

The Australian Competition and Consumer Commission (ACCC) also warns that unsafe pool and spa suction outlets can cause hair or body entrapment, serious injuries and drowning.

Pool owners should ensure that intake grilles remain securely attached, undamaged and free from obstructions. A swim jet with a damaged, loose or missing protective grille should not be operated until the problem has been corrected according to the manufacturer's instructions.

Swim Jet Water Intake vs. Pool Skimmer vs. Main Drain

Although these components all allow pool water to enter a hydraulic system, they perform different functions.

A swim jet intake primarily supports counter-current propulsion, whereas skimmers and main suction outlets typically serve the pool's filtration and water circulation system.

In Australian pool terminology, a main drain generally refers to a submerged suction outlet rather than an opening used primarily to empty the pool.

These systems may operate within the same swimming pool, but their hydraulic connections, flow requirements and protective arrangements should not be treated as interchangeable.