“Wet” & “Dry” Rain Harvesting Systems: What’s the Difference?

Rain Harvesting systems fall into two broad categories: “wet” systems and “dry” systems. 

Whether your system is wet or dry depends on the pipework that leads to your tank.  

In wet systems, the pipes from your gutters travel underground before emerging to empty into your tank. Because these pipes sit below the level of your tank inlets, they remain filled with water at all times (unless you take steps to empty them).  

In contrast, the pipes in dry systems run directly from your gutters into your tank. They fully empty each time after it rains.  

Both wet and dry Rain Harvesting systems have strengths and weaknesses, however with a little planning you can optimise either system to harvest cleaner rainwater and lots of it.  

Wet systems 

Wet rain harvesting systems are often used in areas where water is scarce and unpredictable. These systems collect water that falls on rooftops, streets, and other surfaces, and then collect it in a reservoir for later use. This water can be used for irrigation or drinking purposes.

The greatest benefit of wet systems over dry systems is that they tend to be less aesthetically “messy”, as any convoluted piping is hidden, out of sight, underground. This is particularly beneficial when you have a large or complicated collection of pipes running from your roof.  

Wet systems also allow you to place your tanks further away from your home, which may be a better choice from a practical or aesthetic point of view.  

However, the pipes in wet systems are particularly vulnerable to mosquito infestations and anaerobic fermentation. For this reason, it’s important to take steps to screen your pipes and to empty them after it rains. This effectively transforms your wet system into a dry system, while still allowing you to enjoy the usual wet system benefits.  

You can read about wet systems in more detail here.

Dry systems 

The greatest benefit of dry systems is their simplicity – your pipes run from your gutters to your tank and they empty themselves each time it rains.  

If you’re happy to place your tank close to your home and you’re happy for all the pipework to be visible, a dry system may be the right choice for you.  

However, if a dry Rain Harvesting system is not appropriate, you can use a wet Rain Harvesting system but drain it between rainfall events so you can enjoy the best of both worlds, wet and dry.  

Read about dry systems in more detail here. 

The Right System for You 

Choosing between a wet or dry system will depend on your circumstances and personal preferences.  

Whatever you choose, it’s important to take steps to protect the quality of the rainwater you harvest and ensure you capture as much water as possible.  

Check out our standard Rain Harvesting system designs to learn more about how you can ensure your wet or dry Rain Harvesting system is optimised to harvest cleaner rainwater and lots of it. These designs can be applied to new Rain Harvesting systems or adapted to upgrade existing ones with minimal hassle.