Waterways Environmental are registered designers and installers of Hydromax Siphonic Drainage systems by Polypipe Terrain. Designers have gone through an intense training course and are capable of dealing with the most complex roof areas in the industry. All designs are in full compliance with BS EN 12056 -3:2000 & BS EN 8490:2007.

The Polypipe Terrain HDPE pipework system (FUZE) used with our systems is also used for gravity rainwater systems and soil and waste systems and is BBA certified.

Our self-cleaning, high velocity siphonic rainwater systems provide an advanced roof drainage solution which can be used to drain large roof areas. Used on applications such as stadia, hotels, leisure centres, apartment blocks, office blocks, factories, hospitals and shopping centres, it offers a complete and proven way of removing large volumes of rainwater from roofs in a controlled manner.

With a gravity flow drainage system, capacity is limited as only one-third of the pipe diameter is used for water flow, which adheres to the inner pipe wall, while a large two thirds is air core. A siphonic drainage system is different, air is purged from the pipe so that it runs 100% full of water, enabling smaller diameter pipes to remove much higher volumes of rainwater.

Designed to accommodate recent changes in storm patterns, as stipulated in BS EN 12056-3:2000, it uses the naturally induced siphonic principles to ‘suck’ the rainwater from the roof into small diameter pipes, creating a flow capacity up to ten times greater than that of an equivalent gravity-fed system.

We fully understand how important it is to have design freedom so our discreet pipe work can be installed horizontally without a slope, giving you the freedom to decide on ceiling heights and where you want the downpipe locations to go.

This also enables a significant reduction in underground drainage, trenching, soil removal, treatment of backfill and often means no drainage is required under the building floor slab.

Siphonic drainage advantages are:

  • Fewer siphonic drains are required therefore reducing roof penetrations
  • Rows of vertical rainwater pipes inside a building are eliminated, together with the extensive under floor drainage systems to serve them
  • Fall or gradient is not required to transport a siphonic flow
  • The location to siphonic drains on the roof or in a gutter is not restricted to column positions
  • Siphonic systems can be integrated with roof, gutter and underground drainage design to produce optimum solutions to known parameters
  • The discharge from each siphonic downpipe is a specific water volume at a pre-determined location in the building envelope
  • Siphonic drains are performance tested and calibrated for flow capacity and operational water depth


For more information, please view the video below on how the system operates and download our brochure on the system on the right.


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