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Last updated Mon 16 May 2022

A cistern is a receptacle for holding liquids that is waterproof, effectively making them a type of covered reservoir. They can be distinguished from wells by their waterproof linings, as these linings dramatically change the functionality of each device. As the walls of a cistern are waterproof, it is typically used to catch and store rainwater, while the non-waterproof walls of a well allow it to draw from groundwater.

Aptus Plumbing Cistern
Aptus Plumbing Cistern

Early Cisterns

Cisterns were present in a diverse range of cultures, and as each culture developed the cistern independently of each other, this is an example of 'multiple discovery'. The earliest known examples of lime plaster cisterns date as far back as the Neolithic era, where they were rare oddities of early plumbing, though by the time of Ancient Rome, cisterns were built in most houses. Unfortunately, this practice was lost with the rest of Ancient Rome's plumbing systems, and by the Middle Ages, Europeans typically only built cisterns inside of their sprawling castles, and they were only used where wells could not be dug.

Notably, the Middle Age Europeans did make use of filter cisterns in addition to tank cisterns, with a notable example being built in modern-day Austria out of lava rock. This cistern featured a filter made of sand that the water passed through, and the filter both cleaned the water and enriched it with minerals.

Modern Cisterns

Cisterns are still used extensively in the modern-day, especially as the expansion of plumbing technology now demands more and more water be available to homes for day-to-day use. The toilet cistern is an example of a cistern found in most Western homes, though rainwater cisterns are also used extensively anywhere that water is hard to find, such as the Australian wilderness.

While cisterns were once used for cooking, cleaning, and irrigation purposes, modern concerns of water quality have left most cisterns to be used only to collect and store either wastewater or water intended for irrigation. However, there are many products available to help filter or purify cistern water if it is intended for human consumption, helping alleviate water pressure in locations that are suffering from drought. Cisterns that collect rainwater also need to ensure that their rainwater-collection systems do not provide conditions suitable for the growth of algae or the attraction of mosquitoes, as both can prove harmful for human life.

To this end, cisterns are kept clean to a strict standard, especially when they are storing water that is intended for human consumption. To ensure they are well-maintained, cisterns need to be regularly inspected and kept enclosed, and must be routinely flushed with a solution of diluted chlorine.

In some countries, such as Brazil, the cistern sits either atop of the house or on higher ground, so that it can use gravity to supply the running water needs of the home. These cisterns are typically not filled with rainwater but rather by electric pumps supplying well-water, or they can be manually filled by a truck delivery. Such cisterns are typically made out of concrete walls, with a piece at the top that can be removed while the cistern is being filled and replaced afterwards to ensure that insects, debris, and other waste cannot enter the cistern.

This toilet has a cistern hidden in the wall
This toilet has a cistern hidden in the wall

Toilet Cisterns

The cistern of a toilet is designed to hold the right amount of water for a full flush cycle. In the past, these cisterns were suspended above the toilet and connected by a long pipe, but modern toilets typically see the cistern mounted directly onto the toilet bowl. In some cases, such as the urinals found in male toilets, the cistern may instead be hidden in the wall, which is known as a 'concealed cistern toilet'. Similarly, some cisterns service more than one toilet bowl at once, and these cisterns are called 'flushing troughs'.

Alternate Uses For Cisterns

Cisterns are also popular additions to greenhouses, as they can help keep the costs of irrigation down and decrease the demand on the public water supply. As a result of these benefits, some countries, such as the United States of America, have implemented laws that mandate the construction of rainwater harvesting systems alongside all other new building projects, and in these cases, a cistern may be used. Some other countries, such as Japan and Spain, are less aggressive in their legislation around cisterns, though they do provide tax benefits to those installing them on their properties.

Some cities and towns also use underground cisterns to provide fire-fighters with access to water in circumstances that they otherwise wouldn't be able to access any. San Francisco in the United States of America is a notable example of this practice, with various fire cisterns dotted throughout their streets in the event there is a disruption to the city's primary water supply. Similarly, overflow cisterns are used in some urban areas where pavement has made it hard for water to be absorbed back into the water table, and the excess has now made it difficult for sewage and drainage systems to cope with excessive rainfall.

This cistern is hanging above the toilet
This cistern is hanging above the toilet

This cistern is connected directly to the toilet
This cistern is connected directly to the toilet


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