Greywater Systems: Flushing the Toilet with Your Shower

 


Greywater Systems: Flushing the Toilet with Your Shower

Why you might be flushing away perfectly good water – and what to do about it.

 What Is Greywater?

Greywater is the gently used water from:

  • Showers

  • Baths

  • Bathroom sinks

  • Washing machines

It’s not clean enough to drink, but it’s not filthy either – and it’s perfect for flushing toilets or watering plants.

In fact, toilets don’t need fresh drinking water. But that’s what we use. Every single flush.

Why Flushing with Greywater Makes Sense

  • Toilets account for 30% of household water use

  • In the UK, that’s over 30 litres per person per day

  • And we’re using drinking water for it!

Meanwhile, that warm shower water just disappears down the drain.

Why not redirect it?

How Greywater Systems Work

There are several levels of complexity:

Basic Manual System

  • Collect greywater in a bucket (e.g. from your bath or shower)

  • Pour into the toilet cistern or directly into the bowl

Pros: Cheap, easy
Cons: Bit of a faff

Semi-Automated System

  • Divert shower or washing machine waste into a small holding tank

  • Use a gravity-fed or pumped system to refill toilet cisterns

Pros: Efficient, saves lots of water
Cons: Needs filters, maintenance, plumbing know-how

Full Domestic Greywater System

  • Filters and treats greywater before automatic reuse

Pros: Invisible, automated
Cons: Expensive to install, planning permission may be needed

Isn’t It... Gross?

Greywater isn’t sewage. That’s blackwater (from toilets and kitchen sinks).

Greywater may contain:

  • Hair

  • Soap

  • Detergent residue

But with basic filtering and responsible product use (e.g. eco-friendly soaps), it’s safe to reuse for flushing and irrigation.

Benefits of Greywater Reuse

  • Cuts water usage by up to 40%

  • Lowers water bills

  • Reduces strain on sewage systems and treatment plants

  • Water your garden even during hosepipe bans

  • Helps rethink what ‘waste’ means

Important Tips

  • Don’t store greywater for more than 24 hours – it goes smelly

  • Avoid using it on edible plant parts unless it’s filtered

  • Stick to biodegradable, plant-based soaps and detergents

  • Check local building codes before installing permanent systems

Final Thought

You wouldn’t pour fresh bottled water into the toilet…
But that’s essentially what we do every day.

Greywater systems make us rethink our relationship with water — and once you start saving, you won’t want to stop.

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