Plumbing tips to prevent an overflow of wastewater

With multiple one-in-100-year floods this year, things are not getting any easier on our water infrastructure in many parts of the country.

Excess rain means excess of stormwater, and if that finds its way into the wastewater system it can have devastating consequences for those living nearby.

That’s because if stormwater systems overflow, excess water can enter the sewerage system and if enough of it does, it can trigger an overflow of wastewater.

Wastewater is water discharged from homes and businesses, carrying with it not only human waste but residue of products like soap or laundry detergent. Unlike stormwater, it needs to be treated.

Because if untreated wastewater flows outside of the sewerage system, it can not only impact the health of people who come into contact with it, but also our aquatic ecosystems.

If you have been flooded, first contact your local council for help; if you're in Auckland and that mess is wastewater, contact Watercare. Unless you caused the mess, Watercare will clean up.

Because they are intended to go to different places, wastewater and stormwater leave your house in different ways – stormwater via a downpipe, and wastewater via a gully trap.

You may not have heard of a gully trap before, but you wouldn’t want to be without one. Gully traps are basins in the ground, that collect wastewater, before it enters the sewer system. Your toilet has a pipe of its own, but the rest of the water from your sinks, shower, and washing machine all flow to the gully trap.

They have a water seal to keep foul odours from the sewer out of your house and can usually be found outside, against a wall that connects to your kitchen, bathroom, or laundry.

Gully traps should be raised from the ground to keep out groundwater and be covered by a grate, to keep it from getting clogged with detritus.

It’s good practice to regularly check your gully trap is clear of blockages – if you look under the grate it should be clear of dirt or leaves. A plumber can raise a gully trap if need be, and clear a blocked pipe no problem.

Downpipes pipe rainwater directly from your roof into the stormwater network. It’s crucial these just connect to the stormwater network, and are not releasing stormwater into the gully trap, or pouring it on your lawn or driveway. A downpipe that leads to a gully trap is sending a lot of stormwater into the wastewater system, and that can contribute to overflow.

If your downpipe is non-compliant, talk to a plumber about moving it. Depending on where it is, that could mean less groundwater for you, and less burden on those who live downstream.

When trying to reduce the strain on your drain – watch out for solid waste and oils. Nothing solid should go down your drains – that means keeping as much food waste out of your kitchen sink as you can. You should also make sure any tissues or paper towels go in the bin or the fireplace. Toilet paper is designed to break down in water, so it can be flushed down most toilets without a problem. And keep sanitary products out of your toilet.

Even though it may not be solid at room temperature, any fat or oil should also be kept out of your pipes. Fats can coagulate into what is referred to as a “fatberg,” a solid structure of fat mixed with other non-biodegradable items that have found their way into the drain. These restrict the volume of water that can flow through the pipe, which means overflow can happen more quickly.

So what can you do with leftover cooking oil? Your best bet is to put it in a sealed container once it cools, and then throw it in the bin with your regular rubbish. It may not be glamorous, but keeping a container of oil on your bench until it fills up - rather than throwing each batch of oil away separately - is a great way to cut down on waste.

If you are looking at buying a house, consider having the pipes checked out as part of your due diligence. Older houses can have plumbing leaks, tree roots growing through pipes, or clogs that have built up over the years which may come back to bite you in future. These could be costly to repair, so find out what is waiting for you before you move in and avoid being surprised by a clogged drain.

The changing climate means that our weather patterns are changing too, and this year Aotearoa has already received more than its fair share of rain. What is being done to help our infrastructure handle the deluge?

Water Service Reforms are planned to be introduced by 2026. That means the way that water infrastructure is managed is changing, but it may not mean an upgrade for your local sewerage or stormwater system.

So take care with what you put down your drains, and make sure they lead to the right place. This is a change you can make now to ensure your plumbing doesn’t become your neighbours’ problem.