When experiencing water scarcity in your area, using six liters of fresh water each time you flush the toilet can leave your tanks dry and empty sooner than you think.

Fortunately, you can minimize water wastage by recycling bath water to flush your toilets. But how exactly do you flush the toilet using bath water?

You can use bath water to flush your toilets with the gravity flush method. To do this, pump bath water into a storage tank at a higher level than the toilet tank and connect the two tanks using a hose.

Water flows through gravity from the storage tank into the toilet tank, and you flush normally.

This article will explore four ways to flush the toilet using bath water. Keep reading to find out which works best for you!

1. Gravity Flush Method

Up close of a white porcelain flushing toilet with bath water

The gravity flush method takes some water harvesting and pumping but allows you to use bath water to flush your toilet as you usually would.

The gravity flush method is the most efficient method of flushing the toilet using bath water.

It’s comparable to flushing with fresh water. However, it comprises a bath water storage compartment that links to the cistern.

Once you flush the toilet, bath water rushes from the storage tank into the toilet tank via gravity until it reaches the required level. Then, the toilet is ready for the next flush.

How the Gravity Flush Method Works

For this method to be efficient, you have to integrate the bath water system into the toilet system using the following procedure:

1. Harvest Bath Water in a Bathtub

Every bathroom has an opening on the floor that drains bath water into the sewer.

First, you’ll have to block the opening. You can use a drain stopper, a rubber material that perfectly plugs the drain for an adjustable solution, or cement the drain if you want a permanent solution.

Once you block the drain, create a piping system that channels the water into the bathtub.

Filling the bathtub with water with the words Fill The Tub at the bottom

Remember, bath water contains contaminants such as soap, hair, and dead skin that can cause problems in your flushing system. Therefore, you’ll need a filter at one end of the pipe.

You can improvise by tying a piece of cloth at the end of the pipe. For commercial filters, you can consider the following options:

Hair Catcher Shower Drain: This filter comes in three bowl-shaped plugs of different sizes. Its small micro-perforations prevent hair and other debris in the water from passing through while allowing water to flow unobstructed.
The outstanding feature of this filter is its ability to withstand corrosion for a long time despite being in constant contact with water.

Inline Pipe Filter: This is the ideal filter if you have PVC or PPR pipes. You connect it along the water passage of the pipe. It comes with a filter strainer, an outer shell, and a top cover that connects the ends that bring water into and out of the filter.
You can easily disconnect the filter from the pipe and wash it.

Note: Irrespective of the type of filter you use, you’ll have to do regular maintenance to remove the trapped dirt and debris. Overlooking this practice causes the pipes to clog, and the bath water will remain stagnant, causing your bathroom to flood.

2. Pump Water from the Bathtub into the Storage Tank

The bathtub should have a delivery port that connects it to the storage tank through a pipe.

Technically, the storage tank should be higher than the bathtub and the cistern (toilet tank). As such, it’ll be impossible for water to flow naturally from the bathtub to the storage tank.

Therefore, you’ll need to install a pumping system, which can be manual or automatic. You can mount the pump on the wall or the floor, depending on your preferences.

a top down view of the inside of a dirty brown toilet tank

3. Hold the Bath Water in the Storage Tank

Pushing bath water directly into the toilet tank is not advisable because it’s not clean and may damage the flushing mechanism.

Also, when the pressure reduces in the toilet tank, the bath water can get suctioned back into the freshwater system. That’s why it’s crucial to have a separate storage tank.

On average, a shower lasting for seven to eight minutes uses 30 gallons (136 liters) of water. If you take a bath twice a day, you’ll use 60 gallons (273 liters).

Your storage tank should be large enough to hold your bath water. If all your bath water can’t fit into the storage tank, you should have an outlet draining excess water into the sewer.

If your bath water remains for more than three days, it can become slimy and allow microbes such as algae and bacteria to grow.

Use water disinfectants such as iodine or chlorine to prevent this. But iodine is the most effective at killing pathogens at the pH of bath water — it takes one to two minutes.

To learn more about wastewater treatment, read this article: Greywater Filtration And Treatment: 6 Details To Know.

4. Flush the Toilet

Flushing the toilet using bath water in a storage tank uses the gurgle principle.

When you open the valve that connects the storage tank and the toilet tank, water gurgles into the toilet tank only when it’s empty.

You flush the toilet as you would while using fresh water.

When the cistern empties water into the toilet bowl, the bath water flows through gravity from the storage tank to the cistern for the next flush.

2. Pour Bath Water Directly into the Toilet Bowl

This method doesn’t require a toilet flushing system.

You can rely on it when you don’t intend to use bath water to flush your toilet permanently or when you want to use fresh water partly and bath water partly.

However, it’s as simple and efficient as flushing using the toilet system.

Like the previous method, you’ll have to install a system for collecting your bath water.

You can also get a storage tank, but instead of connecting it to the toilet tank, make a tap at the bottom to easily fetch water into the container you’ll use to flush the toilet.

pouring water directly into the toilet bowl to force it to flush
While it’s not fun, this is how you flush a toilet manually.

The picture above shows me flushing the toilet manually. Grab any bucket-type of thing you have around the house and fill it with water, and pour directly in.

This is what we have to do during hurricanes as well if the water is out (we fill the bathrubs full with water before the storm comes).

To flush the toilet, proceed as follows:

  1. Transfer one to two gallons (four to eight liters) of water into a bucket. If you’ve stored your bath water in an open container or a large bucket, you can use a jug to fill the bucket.
  2. Remove the toilet lid to get a larger opening for pouring water.
  3. After using the toilet, pour the water slowly, increase the speed gradually, and dump all the water into the toilet bowl.
  4. If waste remains, add more bath water to the bucket and repeat the process until the waste drains away.

Doing this fills the siphon tube, which automatically sucks the waste out of the toilet bowl into the sewer line.

Once the bowl is empty, air flows into the siphon tube, producing a gurgling sound, and the siphoning stops.

Note: If you store your bath water for more than two days, you’ll have to treat it using chlorine or iodine to kill microbes and remove foul odor.

You’ll also have to install a filter to remove hair and other debris in bath water that can damage your toilet flushing system.

3. Pour Bath Water Into the Toilet Tank

Instead of connecting bath water to the toilet flushing system like in the first method, you can pour water manually into the toilet tank and flush as you normally would.

But this method only works if you use a gravity-fed flushing system.

If your toilet has an electric pumping system, using this method can cause your toilet to overflow or malfunction.

However, you can look for a professional plumber to help set up your toilet to work through this method.

Below are the steps to follow when flushing the toilet using this method:

  1. Collect filtered bath water in the bathtub and transfer it to a storage reservoir, a tank, or a bucket.
  2. Open the toilet tank lid.
  3. Cut off the freshwater supply in the toilet tank by turning off the freshwater valve.
  4. If the toilet tank has fresh water, flush it to leave the tank empty. Because you’ve disconnected the fresh water supply, the toilet tank won’t automatically refill.
  5. Transfer bath water from the storage into the toilet tank using a jug or a bucket up to the watermark. The average volume needed is six liters (1.6 gallons), but it may vary slightly depending on your toilet model.
  6. After using the toilet, flush it as you usually do. This should carry the waste away.
  7. Close the toilet lid and repeat the process the next time you use the toilet. Don’t let bath water remain in the toilet tank because it contains chemicals that may affect the normal functioning of the toilet or damage the plumbing system.

4.  Use a Pump System

Instead of using gravity like the standard toilet flushing system, this method uses pressure from a pump to push the waste from the toilet bowl into the sewer.

It works regardless of where you place the storage tank, which means you can collect bath water directly into a storage tank after filtering without first channeling it into a bathtub.

You’ll also have to connect the storage tank to the pumping system around the toilet area. Simply press the pump lever to flush the toilet.

Doing this pressurizes the bath water in the storage tank and forces it into the toilet bowl, flushing the waste into the sewer system. If the waste fails to flush, repeat the process.

Note: When using bath water to flush your toilet, cleaning the tank is equally important as cleaning the bowl. Bath water can cause rust and discoloration to the interior parts of the tank.

To effectively wash the toilet tank, you should soak it with vinegar overnight, scrub it, and rinse it with fresh water at least twice a month.

5. Install a Gray Water System

A gray water system uses water from various household sources, excluding water contaminated with fecal matter (black water). Bathwater, which typically contains soap, shampoo, and skin cells, is considered gray water and can be used for flushing toilets.

Here’s an overview of how to use a gray water system to convert bathwater into toilet flushing water:

  • Collection and diversion: Install a separate drainage system that directs bathwater to a collection point. You can install a diverter valve to allow the choice between sending water to the sewer or redirecting it to the gray water system.
  • Filtration: Use a filter or mesh system to remove larger particles such as hair and debris.
  • Chemical treatment: Additional treatment may be necessary, depending on the chemicals in bath products. You can use iodine or chlorine as already discussed.
  • Storage tank: Install a storage tank to hold the treated gray water until it is needed for toilet flushing. The tank should have a level sensor to ensure proper management of water levels.
  • Pump System: Integrate a pump system to move water from the storage tank to the toilet flushing system. The pump may be activated automatically when the toilet is flushed or manually, depending on the system design.
  • Distribution system: Design a distribution system that delivers the gray water to toilets. The system should comply with local regulations and building codes.
  • Dual plumbing system: If you’re building a new house, consider implementing a dual plumbing system with separate pipes for black water and gray water. The system will simplify the installation of a gray water system.
  • Safety considerations: Label the pipes clearly to differentiate between gray water and potable water to avoid confusion.

Final Thoughts

More than 20 percent of domestic water usage goes to the bathroom.

Recycling bath water in the toilet can help minimize fresh water wastage, especially if you live in an area that regularly experiences water shortages.

Fortunately, flushing the toilet using bath water is an easy process that works efficiently with a bit of improvisation.

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