Mains Top-Up Units

WISY Mains Water Top-up

Most rainwater harvesting systems require a means of switching to an alternative water source, in the event of the system running out of rainwater. However, there are strict regulations governing the way that this is done, in order to eliminate any risk of non-potable water being able to siphon back into the mains supply. This is achieved through the use of an air gap that the mains water must pass through before entering the tank. The WISY mains top-up assembly provides an AA air gap designed specifically to meet this requirement.

Advantages of GRP Tanks

  • ​The water supply into the tundish is regulated by a solenoid valve which is connected electrically to a float switch or level sensor.
  • Each assembly also includes a flexible braided connecting hose for ease of installation, and an isolating valve with integral dirt strainer to protect the solenoid valve.
  • The stainless steel tundish incorporates a laminar flow device to ensure that a vertical splash-free column of water passes through.


  • These mains top up units can also be used in indirect systems for filling a header or break tank in the same way.
  • Five models are available, to fit following pipe sizes: 1/2″, 3/4″, 1″, 11/2″ and 2″
  • Complies with EN 1717.

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