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WFP System Delivery Unit Types Explained

The delivery unit you need depends on the way you want to obtain pure water and the type of water area (hard or soft) you’re in. There’s the choice between on-board filtration or getting your tank filled with ready-made pure water. Soft water needs less filtration than hard water. Here we describe your options and highlight the main advantages or disadvantages of each.


Delivery Only Unit

As the name implies, a delivery unit is a system without any onboard filtration to purify water. In essence it is just a holding tank for the pure water which you buy in from a pure water filling company, OR you fill up from your own Static Unit (see below). Only pumps, temperature controllers and a battery to run them are needed on the system.



  • No filtration on board means reduced weight in the van, so that other items like trolleys and gutter vacuums can be stored in the van as well.
  • Filtration equipment is expensive. Using ready-made Pure Water (bought in or made in a Static Unit rather than a moving van) can reduce maintenance and repairs significantly.


  • You’ll need to get back to base or a filling station when the tank is empty.

DI Unit

A DI (De-Ionisation) unit is similar to a delivery unit but with the addition of DI Resin vessels to purify the water.

DI Units are mainly used in Soft water areas where the TDS (Total Dissolvable Solids) in the home & commercial water supply is below 120 PPM (Particles Per Million). Where the TDS is between 0 and 60 you need one 11ltr DI vessel; where the TDS is between 60 and 120 two 11ltr DI vessels should be used.

You just fill you tank with water from your home supply and on the way out to the job you intersect with the DI vessels for the purity. This system comes with an electronic float system and digital controller - once the float is horizontal a signal goes to the controller which then closes the solenoid valve to prevent overfilling.



  • You can make all the Pure Water you need on the spot from the tap water supply
  • Prevent overfilling with the electronic float & digital controller


  • This system can’t be used in Hard Water areas.

RO Unit

A RO (Reverse Osmosis) unit makes purified water on the spot. They’re used more in hard water areas, where the TDS is from 120-400+ PPM.

This type of unit is a bit more complex as it requires 5 types of filtration to make the purified water. The first three are a Sediment filter; a Carbon Filter and a Mixed Sediment/Carbon Filter. These first 3 filters are for removing the larger particles and chemicals in the mains water.

The next filter is the actual RO membrane which on its on can remove 92-96% of all water particles. The RO membrane is the most expensive filtration item. The first three filters are needed to protect the RO membrane from becoming clogged up.

Finally, there’s a DI filter which will take the remaining particles from the water to create a 0 PPM reading.

Ideally, this system should be fitted with an Autofill/Auto flush digital controller system. By pressing one button on the controller this not only fills the tank but also flushes the system periodically during the fill cycle. It will do this for 5 minutes every hour, saving time on the maintenance flush cycle that otherwise needs to be carried out every other, making it very low maintenance.



  • You can make all the Pure Water you need on the spot from the tap water supply, even in a hard water area. No need to return to base to refill.
  • Autofill/flush system makes this very low maintenance


  • This system is heavier so you need a heavier payload van, or there’s less capacity for other equipment in the van
  • Filter parts are expensive - as they’re set up in a working vehicle the chance of breakages increases

Static Unit

A Static unit is basically the RO system stored in a unit or designated building with the addition of a holding tank to store the pure water. You then filling your Delivery unit with pure water. Depending on what space you have you can make & store thousands of litres of Pure Water and use it as as needed.

  • You can make all the Pure Water you need from the tap water supply and store to use as needed
  • All the expensive filter parts are safe in a building rather than in a moving vehicle – the chance of breakages is drastically reduced.
  • You need the space to set up the Static Unit
  • You need to go back to base to refill every time your Delivery Unit is empty

Trolley System window cleaning trolley

This is effectively the same a Delivery Only Unit, filled from a Pure Water source or directly from your vehicle tank with a fastfill system. They’re wheeled, lightweight and very handy for those awkward jobs where you can access with the Trolley rather than reeling out 100m plus of hose.


These are also ideal if you've just started your company on a small budget, before your business takes off and you can advance to a larger system.



  • Inexpensive, lightweight & easy to manoeuvre.


  • Smaller capacity means you need to refill more often

Here at Toolcraft, we can build all these systems to spec; creating a tank made to fit your van together with all filtration needed. What are you waiting for ?

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