A Basic Guide To Cistern Plumbing

A Basic Guide To Cistern Plumbing

Ian Mutuli
Updated on
Ian Mutuli

Ian Mutuli

Founder and Managing Editor of Archute. He is also a graduate architect from The University of Nairobi, Kenya.
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A functional toilet is something that's often taken for granted. It allows people to dispose of waste in a convenient and hygienic way, making it an essential fixture in your household cistern water system. 

Since it sees a lot of household use, there will be times that your toilet may act up. Most homeowners have experienced toilet leaks, water quality problems, or instances where the toilet won’t flush. It’s best to be prepared for this by understanding your home's cistern water systems—specifically, your toilet’s plumbing system.

Many toilet issues involve the cistern system. The primary function of the cistern is to store water for flushing—in other words, it acts as a storage reservoir. The cistern pushes the collected water into the bowl, flushes it out, and refills it with clean water.

Over time, parts of the cistern water system may get old and break. Parts of modern cisterns are often replaceable. However, if the damage concerns the entire cistern water system due to cracks or leaking, you might need to replace it altogether. In that case, call a reliable plumbing company and let them handle the cisterns replacement process.

To learn more about the cistern system, continue reading this post.

What are the Components of a Cistern?

Several essential parts comprise a functional toilet cistern system for efficient water management. As components of flushing toilets, the following parts take the collected water out of the bowl and refill it with clean water:

  • Filling Valve


    The filling valve is connected to a water line beneath the tank, and water passes through it to enter the storage tank. It opens when the water supply inside the tank is too low and closes once the collected water within the storage tank reaches the optimum level.
  • Float Mechanism


    The float mechanism is connected to the filling valve and regulates the cistern water supply. The float device rises and falls with the water level, automatically opening and closing the filling valve based on the cistern water level. This is important because if the water inside the tank is below the optimal level, there's not enough water to make the cistern water system work.
    Alternatively, the float mechanism ensures the cistern water supply doesn't overflow. Once the water collected reaches a certain point, the rising float device causes the fill pipe to close.
  • Overflow Pipe


    This is a necessary safety feature in the cistern system, as it prevents water from spilling out in case the fill valve or float mechanism malfunctions. The overflow pipe redirects the excess water to the toilet bowl, preventing potential water damage and maintaining the efficiency of your home's water system.

How Does the Toilet Cisterns Function?

When you press the flush button, the cistern pushes the supply water out of the tank and into the toilet bowl. This process is often aided by air pressure or gravity, which is why most basic toilets are called gravity flow toilets.

After flushing, the float mechanism will trigger the filling valve and keep it open until there’s enough water supply inside the cisterns tank. The water in the storage reservoir will be ready for subsequent household use.

Plumber repairing toilet cistern at water closet

The water supply required to fill the cisterns tank may vary depending on your toilet's flush system. There are two types of flush systems: single flush and dual flush.

The main difference is that a single-flush system uses more household water per flush than a dual-flush system, which has two flush buttons—one for liquid waste (e.g., urine) and the other for solid waste (e.g., fecal matter). In addition, a dual-flush system only requires as little as 4.5 liters per flush. Larger cisterns may require more water.

How to Replace Toilet Cisterns

Here’s a step-by-step guide to replacing toilet cistern tanks:

1. Get A New Cistern Tank

Ensure that the cistern you bought is of acceptable quality and compatible with your toilet, as well as the space around the bowl. Smaller cisterns, for instance, would not be ideal for big toilet bowls.

2. Empty the Old Cistern

Before you begin the actual replacement, switch off the cistern water supply. This can be done at the filling valve or your home's main water supply. Then flush the toilet to empty the cistern water. Since the water supply is switched off, the cistern water will not be refilled.

3. Remove The Old Cistern Tank

Undo the nut connecting the cistern and the water supply. Then undo the other nuts securing the cistern to the bowl. After removing all these, you can lift the cistern off the toilet bowl.

4. Install the New Cistern Tank

If the new cistern is compatible with your toilet, you can easily reverse-engineer the process. Position the new cistern over the toilet and reattach the nuts and screws to the cistern. Don't forget to secure the cistern water supply line afterward.

Even if you've hired a plumber to handle the replacement, it's essential to know the process and how to make a cistern water system work efficiently.

What are the Issues that Might Signal a Damaged Cistern?

Plumber repairing a toilet cistern

Here are common problems homeowners encounter with cistern systems:

  • Faulty or Incomplete Flush

    If your toilet doesn’t flush properly, the cistern water level might be too low due to damage in the cistern system.
  • Fails to Flush Despite Sufficient Cistern Water Level

    This usually occurs when the siphon used to get the cistern water flowing is worn out.
  • Slow Filling

    If it takes a while for water entering the cistern to reach the optimal level, the filling valve might be obstructed or damaged. 

Final Thoughts on Cistern Plumbing

The cistern water system is essential for your toilet to function smoothly. The water supply from the cistern is used for flushing waste and refilling the toilet. When the cistern system is damaged, it’ll be a major inconvenience for you and your family. So, it's important to be aware of how the cistern water system works and how you can ensure that the water supply continues to flow smoothly.

Frequently Asked Questions on Cistern Plumbing

1. What is a cistern used for? 

A toilet cistern, also known as a toilet tank, is used to store and release water for flushing the toilet. It is an essential part of the toilet system, typically attached to the toilet bowl either directly on top or behind it. The cistern holds a specific amount of water that's released when you press the flush button or lever. 

2. What is the difference between a cistern and a toilet? 

The cistern is a component of the toilet system that stores and releases water for flushing. The toilet, on the other hand, is the entire fixture, including the toilet bowl, where waste is collected, and the cistern system, which provides the flushing mechanism. In simple terms, a cistern is a part of the toilet. 

3. What are the different types of cisterns? 

There are various types of cisterns used in toilet systems, including;

  1. Close-coupled cisterns that are directly attached to the toilet bowl, forming a single unit
  2. Low-level cisterns that are connected at a lower level than the toilet bowl with a short flush pipe
  3. High-level cisterns that are mounted high above the toilet bowl and connected with a longer flush pipe, often seen in older or traditional bathrooms
  4. Concealed cisterns that are hidden behind walls or within bathroom furniture, where only the flush button or plate is visible.

4. Can you have a toilet without a cistern? 

Yes, it is possible to have a toilet without a traditional cistern. Some alternatives include wall-hung toilets with concealed cisterns hidden behind the wall and tankless toilets that are directly connected to the water supply and that use a high-pressure valve to flush waste away without the need for a cistern system. 

5. How do you drain a cistern? 

To drain a cistern, you must first turn off the water supply to the toilet. Then flush the toilet to empty the cistern as much as possible. You can use a sponge or towel to soak up any remaining water in the cistern. 

If necessary, disconnect the cistern from the toilet bowl or wall for further cleaning or maintenance. 

6. Can you flush a toilet without a cistern? 

Yes, it is possible to flush a toilet without a cistern system by manually pouring water directly into the toilet bowl. Pouring a sufficient amount of water quickly into the bowl (around one to two gallons) can create enough pressure to initiate a flush. However, this method is less efficient and less convenient than using a cistern system for regular flushing. 

Ian Mutuli

About the author

Ian Mutuli

Founder and Managing Editor of Archute. He is also a graduate architect from The University of Nairobi, Kenya.
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