Saving Water: How to Reuse Your Shower Water to Flush the Toilet

Clean water is a precious resource and has both an environmental and economical cost. Saving it is not always easy as it is an essential factor of modern comfort, but chances are, there is one place in your house where you can easily save water: the toilet. Don't worry, I am not telling you to stop flushing, just to use water in a smart way. Toilet water doesn't need to be of drinkable quality. In fact some parts of the world (Hong Hong, Singapore and Tokyo) have adapted and use sea water in the toilet. Even far from the sea there is plenty of degraded but still usable water you can valorize: the water from your shower, washing machine, etcetera...

In this tutorial i will show you how i set up a system to recuperate the used water from my washroom and reinject it automatically into the toilet's reservoir.

To setup this system you need two essencial componants:

• A pump with pressure tank system
• A reservoir

You will also need a variety of water pipes, taps and connections depending on your home's layout and water pipes.

To re-use domestic water, it needs to be first collected, then reinjected into the toilet's water alimentation circuitry. To do that 4 elements are required:

• A circuitry to collect the used water
• A water tank to store it
• A pump + pressurized reservoir to feed the water to the toilet
• A circuitry to conduct the pressurized water to the toilet

In this step, i will introduce the main considerations related to these 4 elements before giving my own solutions as an example in the following steps. I encourage anyone willing to replicate this setup to think about those points by yourself as the configuration of your house may require you to adopt different solutions than my own.

• Water evacuation is gravity feed to minimize the complexity of the evacuation system and toilet and domestic water are generally separated to minimize odor issues. This means that in a single floor house equipped with a basement, the used water pipes are generally on the roof of the basement easily accessible. That was my case and it makes the whole installation possible. In other configurations you may not be able to implement a similar system.
• The used water needs to be stored to be available when you need it. The storage tank should be big enough to contain all the water you will use between filling (ie shower, washing machine ect...) but not to big to limit the issues with water fouling due to its stagnation in the tank for too long. The temperature and nature of the water will impact the acceptable storage delay. Cloth washing water, strongly charged with detergent can be kept for a long time while manually washed dish water, charged with food residue will degrade faster. Those points should be considered when selecting what used water to re-use. Additives can be added in the reservoir to stop water fouling but be cautious of what product to use if you have a sceptic tank. The average volume of a toilet flush is 6l. To grossly estimate the tank volume required you can count the average number of time your toilet is used in a day, multiply by 6l and add some security margin.
• Various types of pump system exist and could potentially be adapted for water recuperation, however standard toilet filling mechanisms are conceived for a constant pressure input and if you don't want to change it you need a pump with a pressurized water tank. This type of system can be bought for as low as 110 USD (i payed mine 99EUR).
• You will generally need to make a new water circuitry to your toilet as you cannot directly inject used water in the drinkable water circuit. I also encourage you to keep the existing water alimentation system to be able to switch in case of issue.

In the case of my house, the evacuation pipe for the cloth washing machine, the shower and the bathroom sink is directly exposed in the basement under the toilet area. To reuse the water i only need to use a water baril to collect the water and send it back to the toilet via a pipe that I added for this use.

In the next step i will go through each element in more details.

Evacuation systems are made of large diameter PVC pipes. Toilets pipes are generally in 10cm diameter while "normal" water water evacuation is often in 5cm diameter as they have less "solid content" to evacuate. To collect the waste water the most elegant way is to cut your existing pipe and to add a T connection oriented to the bottom. PCV pipes are easy to glue and form water tights joins, you can look here for a demonstration: https://www.youtube.com/watch?v=QQF_XDISuSw&ab_channel=EwingIrrigation%26LandscapeSupply

If you don't feel like doing that you can also pierce the pipe and glue a connector like i did here, but there are a few things to remember. The waste water contains particles and hairs from the showers. Those hairs can agglomerate on small asperities and end up clogging your pipe. For this reason you should thoroughly clean the cut from any chipping left after the cut and keep an access possible for maintenance.

After piercing the "least dirty" method consists in gluing or fixing a T saddle piece on top of your hole use it to connect your collection pipe. Alternatively, you can use a hot gun to form a piece of pipe to the shape of a saddle and glue it on the hole. I did it in this case as I was kind of forced to but I do not recommend it. If you choose this method anyway I recommend to first extend the tip of the pipe using a conical shape before forming it with the pipe it will be glued onto. For examples of PVC heat forming you can look here: https://www.youtube.com/watch?v=xRZzTnd9rko&ab_channel=fearlessdoer

As you may need to dismantle your installation to install or open the reservoir i recommend adding a flexible piece of tube. This will help you for maintenance and can also provide an access point to the connection as it doesn't need to be permanently fixed.

For the water reservoir i used a 120l baril i had in stock, but a few modifications are required. Most pump system will accept particles smaller than 1mm and hairs would not pose a problem to it, but the water valve system in your toilet has a different opinion, and particles can definitely trigger a malfunction of the system causing the water to flow into the toilet until your reservoir becomes empty. For this reason a particle filter is required. To minimize maintenance I elected to install a large filter inside the reservoir (made with a stocking extended on an inox wire armature). The filter and the water output are placed about 20cm higher than the bottom of the tank in order to let the particles decant to the bottom and not to be aspired in the system. I also added a purging hole at the very bottom of the reservoir to remove all the residue once in a while. This method reduces the effective size of your reservoir and facilitate the fouling of the water, it should only be used if you expect a lot of particles in the water (my shower is often used to wash dogs...). Otherwise a simple filter like this: https://www.amazon.com/Winb-Double-Layer-Encryption-Connection-Strainers/dp/B0B35VBMPL/ref=sr_1_12?keywords=water+pump+inlet+hose&qid=1674976606&sprefix=pump+inpu%2Caps%2C290&sr=8-12 placed at the bottom of the tank might be enough.

You may also prefer to add a filter like that: https://www.amazon.com/Sooprinse-Garden-Pressure-Sediment-Attachment/dp/B07Y1JYQJZ/ref=sr_1_11?keywords=water+pump+inlet+hose&qid=1674976606&sprefix=pump+inpu%2Caps%2C290&sr=8-11 later on your installation to have an easier access.

For my installation i made the connections by doubling the tank's walls with a heat formed PVC layer glued with cyanoacrylate (PVC glue doesn't work on the polyethylene tank). I could then pierce and use PVC fittings. This is once again not the cleanest way to do and I would recommend instead bulkhead tank connector like those: https://www.amazon.com/Joywayus-Connector-Theaded-Bulkhead-Stablizing/dp/B07GPP23K9/ref=sr_1_5?crid=NHZYB08AKFL7&keywords=Bulkhead%2Btank%2Bconnector&qid=1674976442&sprefix=bulkhead%2Btank%2Bconnector%2Caps%2C276&sr=8-5&th=1

Pressurized pumping systems can be bought for a few hundred USD online. Those systems are often used to pump water out of a well and are composed of a pump, a tank with a membrane and a pressure control system. The tank is composed of two compartment separated by an elastic membrane. One of the compartment contains water and the other air. When more water is introduced it deforms the membrane and compresses the air. That way the uncompressible water can be stored under pressure. The pressure control system monitors the pressure and start the pump when it drops below the threshold.

For this application a low cost pumping system can be used as there is no need for high pressure (here low pressure only means that the toilet reservoir will be filled more slowly after flushing) and the capacity of the pressurized tank is not important. Furthermore low cost generally mean low pump power and low noise which is a benefit for an installation indoor. However there are two important things to look for: Does your pump includes a one way valve at the input and does it have an automatic stopping mechanism in case the (non pressurized) water reservoir is empty.

The one way valve is not systematically included and is absolutely necessary. Without it the water of the pressurized tank will be driven back to the system input when the pump automatically stops after reaching the threshold pressure. In my case I installed a valve at the input as shown in the picture. The connection to the reservoir upstream of the valve is not pressurized and can be made with classic garden hose.

I do not yet have a water level safety switch to stop the pump and i plan to make one in a future still to be determined. The function of a water level switch is to stop the pump when the reservoir is empty. In its absence the pump will be unable to push enough water in the pressurized tank to reach the threshold and will continue to run indefinitely until breakdown. In the absence of such a switch make sure that your water input is largely superior to the toilet consumption or that you can hear the pump running to be able to react if it stays on for too long.

Like most water pumps, this system needs to be primed (ie. filled with water) to begin pumping. To simplify this step you can put the pump slightly below the water level in the tank and just flush your toilet to open the valve and let the air go out of your system.

To connect to the toilet i elected to keep the existing system and install two valves to be able to select between "recycled" water and drinkable water. This is slightly more complex to install than just re-using the existing pipe but it allows to easily come back to drinkable water in case the pump has an issue. On the pump side it is better to use a portion of flexible tubing to avoid transmitting the pump's vibrations and to make installation and maintenance easier. However that portion of the piping is under pressure (typically 2 to 5 bar depending on your pump) and the pipe and fittings should be adapted (typical garden hose will not age well under those conditions).

As I think I already expressed in this tutorial this is one possible solution to a house specific problem. However I did my best to point out the important points to consider and suggest a solution, so at this point I only have one advice left: think it through and go ahead. Using things I had left in stock I completed this project for under 150USD. Water is already precious and will probably only become more rare in the decade to come so it is quite worth the pain.