Got toilets and A/C? Learn how this innovative cistern can save you water

by Brianna Crandall — July 5, 2017 — What is touted as the “world’s first” cistern to use condensate from air-conditioning units to flush the toilets in a building has been launched by Encore Cistern (Environmental Condensate Recovery). The toilet cistern is suitable for offices, apartments, public buildings, hotels and anywhere with toilets and air-conditioning, whether as a retrofit or new construction.

Director holding a cistern on top of a pool

Encore Director David Davis with Encore cisterns that would save hotels so much water they would fill numerous Olympic-sized swimming pools. Credit Adrian Sherratt Photography. (PRNewsfoto/Encore)

Encore is considered environmentally friendly as it uses a free, sustainable water supply that has previously been drained to waste. In another first for toilet cisterns, Encore allows architects, consultants and specifiers to secure two extra LEED points (under the Water Efficiency category) — the U.S. Green Building Council’s gauge for sustainability.

Encore Technical Director David Davis said:

Air-conditioning units have a pipe that drains all the condensate away. We’ve developed the only cistern that uses this free water to flush the toilet. When you consider how many buildings use air-conditioning globally, billions of liters of condensate water is generated, all of which has been wasted — until now. All buildings need toilets, so why wouldn’t you use a cistern that recycles a free, sustainable water source, especially when there is a global water shortage crisis?

Water savings

As an example, data from hotel specialist STR Global shows 191,832 rooms in 1,477 hotels are currently being built in the United States. Compared to traditional toilet cisterns, using Encore would save the average 130-bed U.S. hotel 3.19 million liters based on standard 80% occupancy levels. In total, Encore would save them 4.7 billion liters of water a year, filling the equivalent of 1,880 Olympic-sized swimming pools.

How it works

Encore holds 18-liters of water — three times more than a conventional cistern, but its dual-chamber design means it fits like standard models. The bottom chamber holds 6 liters, which comes from the mains pipe.  The upper 12-liter chamber is filled with air conditioning condensate. When the toilet is flushed, the lower chamber empties then refills with condensate from the upper chamber.

If there are multiple flushes close together or the air-conditioning is not in use, the cistern is filled by the mains-fed pipe. If the toilet is not used for a period, surplus condensate is fed away.

Where can the cistern be used? Can it be retrofitted?

Encore is designed to be installed as a new build item or as a retrofit to existing toilets. It can be used to replace existing concealed cisterns as long as the existing location can accommodate the increased dimensions of the Encore cistern (485 cm high x 476 cm wide x 195 cm deep). Encore fits all toilets that have a concealed cistern; it is not suitable for close-coupled toilets.

Encore has a unique outlet valve that allows the installer to set the discharge volume to suit local legal requirements, so it is suitable for use around the world. The cistern complies fully with all U.K. regulations, which are in line with most other countries’ regulations, says the company.


Encore was invented by David Davis and Graham Kelly, directors of the U.K.-based G&H Group, a building services company.

Davis added:

For decades, we’ve designed and installed schemes and watched the stream of water produced by air-conditioning units literally go down the drain but not via the toilet. Responsible businesses striving to construct the greenest buildings know how hard [it is] to get LEED points. Gaining two for choosing an Encore cistern is simple and a great advantage.

Visit the Encore Cistern Web site for photos, specifications, and a video of how the cistern works.