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Why Correct Flow Rate and Water Inlet Setup Matter for Pressure Washing

Written by Leona Skene | Nov 21, 2025 12:23:13 AM

Why Correct Flow Rate and Water Inlet Setup Matter

A pressure cleaner is only as good as its water supply.  Even the most powerful SPITWATER machine will struggle if it’s not fed the right volume, pressure and quality of water. 

Taking time to assess your site and set up the inlet correctly prevents faults, improves performance and extends your machine’s lifespan. 

This article covers:

  • Why your water source matters
  • The rules of water inlet set-up
  • What can go wrong
  • Flow rate and pressure- better together
Calculating your minimum required flow rate

Your machine needs a consistent and sufficient flow of water to operate correctly.
If the incoming water supply can't keep up with your machine’s demand, you risk damaging internal components.

General Guidelines

Machine Flow Rate 

Minimum Required Flow 

10 LPM 

12 LPM minimum 

21 LPM 

25 LPM minimum 

30 LPM 

36 LPM minimum 


Rule of thumb
: Supply should be at least 20% more than the machine’s rated flow. This provides a buffer to avoid starvation or cavitation. 

Too much inlet pressure can also be a problem - especially for machines with float valves, which typically max out at around 500 kPa (5 bar). Going beyond this can cause float valves to fail and the unit to leak. 

What to do if flow is too low

If your water supply can’t deliver the minimum flow (e.g. only 15 LPM available but your machine needs 21 LPM), install a buffer tank

Buffer tanks store reserve water to meet demand, preventing dry running and cavitation.

They're especially useful for: 

    • Mobile operators working at multiple unknown sites
    • Sites with intermittent supply
    • Jobs requiring high-flow machines (e.g. 30 LPM+)

SPITWATER offers compatible buffer tanks and low-level water shut-off switches for added protection.  

Recommended hose setup: 

Machine Type 

Pump Type 

Inlet Setup Recommendation 

High-Speed Pump 

Direct fed 

Minimum 7m flexible hose 

Low-Speed Pump + Bypass Cooling Tank 

Gravity/suck 

Minimum 2m flexible hose 

Machines with Bypass Cooling Tank  

Any 

No minimum hose length 
(still must be flexible at final connection)
 

NoteEven if you’re using a short run from a tap, at least the final 2 metres must be flexible.  

What about water hardness? 

Water hardness varies widely across Australia. From 100 ppm on the Gold Coast to over 400 ppm in Adelaide. High mineral content can: 

    • Accelerate scale buildup in hot water coils 
    • Cause abrasion in pumps 
    • Shorten service intervals 

For hardness above 500 ppm, a water softener or chemical dosing pump may be required - especially for hot water machines. 

Water inlet set-up checklist 


◽  Check inlet pressure is within machine specifications

◽  Install a suitable filter between water source and machine

◽  Use a flexible hose of recommended length 

◽  Avoid kinks, sharp bends or restrictions in hose 

◽  Check water quality and address hardness if needed

◽  Test machine under load before starting regular operation

Correct water inlet set-up is a small step that makes a big difference.

By assessing your site and taking these measures, you’ll protect your investment and keep your SPITWATER tough and ready for years of reliable service.