How to access grey water when you've got a concrete house slab

With Australia in the grip of the worst drought in history and Ballarat on yet another year of Stage 4 water restrictions I decided it was time to make use of the grey water produced by our house in an effort to keep the garden and lawn alive through summer.

We are a family of 6 – with 4 kids under 5. Keeping that many small kids in clean clothes means the washing machine is nearly always running. This is clearly the biggest water guzzler in our house using about 140 litres per load. The kids also share a bath once a day using another 70 litres, and my wife and I have a shower each contributing around 120 litres per day. All up this equates to 330 litres of water per day – surely enough to keep the garden looking green.

The problem with accessing this water is that our house is built on a concrete slab. All the plumbing runs under the house inside the slab. By the time the pipe emerges from the slab it has already been mixed with sewerage from the toilets – something I don’t particularly want to put on the garden!

Bath Water
There is only 1 waste pipe that is accessible from outside the house that has not been mixed with sewerage and by shear luck this happens to be the bath. The waste pipe from the bath discharges into the sewer via the ‘gully trap’ – an open, vertical vent in the sewer which is lower than the house but above the ground ensuring any backflow of sewerage caused by a blockage will spew out of it and not up through the showers and all over the bathroom floor!

The bath waste pipe joins the gully trap via a T- join approximately 20cms below ground level on the outside of the house. Tapping into this pipe to capture the bath water would be relatively easy. I purchased a PVC fitting that has a 50mm sleeve on one end, and a threaded 1inch hole on the other. The inside of the ‘T’ was not designed to be joined onto – you are meant to join to the outside of them. As such the inside is not a standard size. Using a heat gun I was able to flair the 50mm sleeve slightly so that I could jam it snuggly into the inside of the join where the bath met the gully trap.

I then threaded a 1 inch fitting into the other end of the PVC fitting to accommodate a poly pipe.

I originally experimented with gravity feeding the water out of the bath as the bath is slightly higher than most of the garden. This was very unsuccessful though as the bath drained very slowly leaving dirt and soap scum behind in the bath. Airlocks were also a big problem – requiring a siphon to be established before the water would drain.

After tweaking the gravity feed system for 12 months I realized it was a lost cause and decided to attach a pump instead. I purchased an inexpensive – yet very powerful pump on eBay. It is a 750w, 240volt, 65Litre/minute pump and only cost $70.

I purchased a plastic tub with lid that was large enough to accommodate the pump. I then dug a hole next to the gully trap and placed the plastic tub and pump in the hole. Being in a hole, the pump is lower than the bath allowing it to gravity feed from the bath to the pump to establish a ‘prime’.

I have built a ground level timber deck down the side of the house where the gully trap is. So the pump sits in its hole under the deck. This meant the tub didn’t need to be UV stabilized or very strong as it never sees sunlight or has any weight on it.

I then ran an extension lead in orange conduit under the deck from the pump to a near-by external power point .

This configuration worked really well. The pump is capable of draining the bath very quickly – quick enough to take all the dirt and scum with the water.

In order to turn the pump on and off, you had to run outside to the power point. This was a bit of a pain. So I purchased a $30 power point remote control from Dick Smith. This has a receiver that plugs into the pump and a transmitter that you can leave in the bathroom. This allows you to operate the pump from inside the house (or from anywhere with in about 20 metres of the pump).

We have now been using the bath pump system for over 12 months and it has worked flawlessly. The bath water alone is enough to keep about 100 square metres of lawn and about 60 plants looking really healthy right through summer.

Shower Water
The next challenge was to find a way to access the shower water. There was no hope of accessing the shower’s waste pipe before it joined the sewer so for about 12 months I thought a practical solution would not be possible.

But then one day whilst in the shower a solution popped into my head that was so obvious I was almost embarrassed that I hadn’t thought of it earlier.

The shower in our main bathroom is next to the bath – the bath that I had previously connected to the pump. Separating the shower from the bath is a 40cm high tiled wall and the shower screen.

My idea was to place a small low voltage bilge pump in the shower and run a ¾ inch pipe between the tiled wall and the shower screen into the bath. I could then pump the water out of the shower into the bath and then from the bath onto the garden.

I tried many different pumps and none worked very well. I tried 2 different types of pond pumps but they both could not handle the soap scum and eventually burnt out. I also tried a cordless rechargeable pump, but this suffered a similar fate.

I eventually found on eBay a 12Volt bilge pump designed for a boat. It is designed to operate in slightly dirty conditions and as such had no problem with the soapy water. Better yet it was only $20!

I unscrewed the grill from the shower waste hole and replaced it with a standard sink plug to stop the water going down the drain. I then placed the bilge pump on top of the plug. The pipe from the pump goes under the show screen (which had to be raised slightly) and into the bath.

A wire was then run from a 12Volt transformer to the pump via a switch in the shower (in an area that doesn’t get wet).

When a person is using the shower they simply flick the switch to activate the pump. The pump is faster than the shower head so it doesn’t need to be on all the time. 2 or 3 20 second bursts of the pump is all that is needed to keep the water level below the top of the shower-base.

Once everyone has had their showers the bath pump can then be activated and the water pumped out onto the garden.

We have been using this system for 12 months now. With this new pump, the system works perfectly. The extra water it provides has made an unbelievable difference to the garden and was well worth the effort.

Washing Machine

The final and biggest water using item in the house is the washing machine. Unfortunately there is no clever way that I can think of to access its water from the outside of the house without running messy pipes through the doors or windows.

So, to many people's shock, I drilled a hole through the brick wall and ran my own pipe! I drilled a 1 inch hole through the brick, the plaster and then through the bottom of the laundry trough cupboard to accommodate a poly pipe. I then connected the discharge pipe from the washing machine to my pipe.

This worked a treat. The washing machine pump was more than powerful enough to pump water 20 metres or so to our front lawn/garden. The only problem was that after the washing machine has drained once, the pipe remains full of water. When the machine begins to fill with water a subsequent time, a siphon exists in the pipe and the water is sucked from the washing machine before it is ready to be drained. This was fixed by adding a simple 'breather' hose in the pipe which allowed air to enter the pipe to break the suction.

Assuming we will always be allowed to wash our clothes and have a shower, our garden is now basically drought proof. While there was a lot of trial and error and a lot of ideas that didn't work, the whole effort was well worth it. We only use the system from November to March which is about 20 weeks. At 330 Litres/day, this equates to over 47,000 litres of water that is now available to our garden each summer that would have otherwise gone down the drain! The parts for the systems I've described above only cost around $300 and even if it only lasts 5 years, that equates to less than 0.1 cents for each litre of grey water. Quite a good investment!