What is a “Wet System”? Rainwater Harvesting Systems

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What is a Wet System? Rainwater Harvesting Systems

When installing a rainwater tank, you will need to consider how to run the piping from your roof to your tank. For this piping, there are two piping systems you can choose between: 1) “Wet System”, or 2) “Dry System”. This article will describe what a “wet system” is and when you would use one with your rainwater tank/s.

What is a “Wet System”?

A wet system refers to the pipework that allows rainwater to flow from your roof into your rainwater tank. What makes a piping system a “wet system” is that after a downpour water is retained in the pipes – hence the “wet”.

Wet systems are comprised of pipework that runs underground to your water tank. Rainwater flows down your roof, into gutters and downpipes which your pipework connects to. This pipework leads underground and eventually joins up to your water tank. If harvesting rainwater from multiple downpipes, they will all meet underground and link up to one large pipe. This large pipe continues until reaching a “riser pipe” where water is then forced up into your storage tank via gravity.

The reason why water remains in the pipes after a downpour is because more water needs to flow into the pipework to pressure water into your tank. When the water stops flowing in, the water in the underground pipework will just remain until the next downpour. This pipework setup is therefore referred to as a “wet system”.

That said, it is possible to turn an underground piping system into a “dry system” – where no water remains in the pipework after rain. Installing an in-ground water diverter at the bottom of the riser pipe will achieve this. Water diverters are intended to “divert” the initial flush of rainwater from your roof (often dirty water) away from your tank into separate storage 60 litres or so. Once this diverted water storage fills up, rainwater then flows on up the riser pipe and into your tank. The reason why no water remains in the pipework is that over time, the diverted water is drained via a slow-release valve. This means any remaining water in the pipework will also eventually drain away.

Benefits of a Wet System

There are several benefits that wet system provides over a dry system:

  • Wet systems are more discrete and so look neater than a dry system. Unlike aboveground pipework, in a wet system minimal pipes are visible – usually only the downpipes that lead into the ground.
  • Multiple downpipes are more easily dealt with in a wet system. Pipe connections can be easily dealt with underground without needing to worry about messy aboveground pipework and getting the right horizontals.
  • A wet system is simpler to install if pipework will be complicated. Aboveground pipework needs to be supported against a building, and there may also be obstacles to navigate around. Awkward joins and corners, different lengths of piping and the like are more easily dealt with underground.

Should You Use a Wet System?

You will generally want to use a wet system for pipework when:

  • your water storage isn’t near to your roof capture area
  • you have a difficult or unclear path from your gutter downpipe to your tank
  • you have multiple downpipes or capture areas that you are harvesting rainwater from.

Wet piping systems can provide an aesthetically pleasing solution for the pipework necessary to feed rainwater into your tank. If you will being installing a rainwater tank, Team Poly supply a wide range of water tanks available with tank fittings and tank accessories including valve, strainer, standalone water diverters (no extra piping needs to be purchased) and more. Contact us today for a free quote or to discuss your needs.