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Can washing machine waste go into rainwater downpipe?

This is a really common question for a lot of people. Maybe you need to move your washing machine to somewhere where the only nearby waste is a rainwater downpipe. Or sometimes people have just moved into a house and the waste is already set up like this and you are wondering if this is okay. Well, wonder no longer. I am here to let you know, once and for all… maybe.

So can it?

I’m afraid the answer is a classic “it depends”. Some houses will be fine to run the washing machine waster into a rainwater downpipe whereas in other houses it wouldn’t be allowed. What this comes down to is how the waste drainage in your house is set up.

This is because washing machine waste shouldn’t go into a separate rainwater drain. Rainwater drains can be separated from the main sewer and instead of going to treatment plants, they run off into rivers, lakes etc. This makes sense, I mean why waste money and energy treating rainwater? If your sewer is set up like this then you definitely don’t want to run your washing machine into it. You will be sending all kinds of cleaning chemicals, grease and other pollutants into the water system.

However, not all houses are set up like this. In fact, in a lot of houses, they still use a shared sewer where everything joins a single sewer that goes to the water treatment plants, including rainwater. If your house is set up like this then you would be fine to use the rainwater downpipe for your washing machine waste as everything is joining one single sewer anyway.

How can you tell what system you have?

One of the key giveaways will be the age of the house. Older houses are much more likely to have a combined sewer whereas newer houses (last 30 years or so) are much more likely to have separate rain and soil sewers. You cannot simply rely on the age of the house to inform you though, you will have to do a little investigation yourself.

The easiest way is to lift your manhole cover for your drains and do a little investigation.

To make sure you have found the sewer drain you should flush your toilet and look for water coming down the drain. If you can see this then you know you have found the sewer pipe. There may be other, brown coloured, giveaways…

Once you are sure you have found the sewer I would advise sending a little dye down your rainwater pipe that you plan to connect to. Then check the manhole and if you can see coloured water flowing then you know that the rainwater flows into the same sewer. If this is the case then you are fine to connect your washing machine waste to this downpipe. If not then it looks like you may have a separate rainwater runoff and you should not connect the washing machine waste to the rainwater pipe.