Flush volume rules are national, and some are set by states or building codes rather than product law. As of October 2026, the US federal limit is 1.6 gallons per flush, England and Wales cap a single flush at 6 litres, Australia requires WELS registration and labelling, and the EU has no single legal limit.
Rules like these change, so treat this article as a starting map. Before you fix the cistern setting on an order, confirm the current rule with your local regulator, certifier or plumbing adviser.
United States
The federal standard is 1.6 gallons per flush (about 6 litres) for WCs, as the US Environmental Protection Agency describes it on its WaterSense pages. Some states set a lower limit. California, for example, has required WCs sold in the state to use no more than 1.28 gallons per flush since 1 January 2016, and other states have similar rules for sales or new construction.
The voluntary WaterSense label also uses 1.28 gallons per flush as its maximum. It is not law, but many retailers and projects ask for it. See WaterSense and Indian toilets.
Every WC sold in the US and Canada must also be certified to ASME A112.19.2/CSA B45.1, which covers flush performance as well as volume. See cUPC and ASME certification.
United Kingdom
In England and Wales, the Water Supply (Water Fittings) Regulations 1999 say no flushing device installed with a WC pan may give a single flush above 6 litres. On a dual-flush device, the smaller flush may not exceed two-thirds of the largest. Northern Ireland's 2009 regulations contain the same limits.
Scotland has its own water byelaws, and Scottish building standards set lower figures for new homes. Check the rule for the nation you sell into. UK buyers often look for WRAS approval to show a fitting complies with the water regulations.
Australia
Under the Water Efficiency Labelling and Standards (WELS) scheme, toilets are regulated products. They must be registered and labelled with a star rating before anyone supplies them, and the duty applies to importers as well as manufacturers. Products must be tested in an accredited laboratory, and plumbing products also need WaterMark certification.
The WELS regulator has set a minimum of 3 stars for dual-flush toilets for new registrations since 17 June 2022. Building rules for new homes can require more. Ratings are based on average flush volume, counting four reduced flushes for each full flush.
European Union
There is no single EU-wide legal cap on WC flush volume. Instead, EN 997 classifies pans by the flush volume they are designed for and sets performance tests at that volume. Class 1 pans work with cisterns of several nominal volumes, from 4 up to 9 litres; Class 2 pans follow the UK-style limits. EN 997 and imported WCs explains the classes.
Member states, regions and green building schemes may add their own requirements. Ask your distributor or a local plumbing body what the market expects, and get the class and flush volume stated on the factory's test report.
Other markets
Gulf, African and Asian markets each have their own approach. Some set limits through building codes, some through product conformity schemes, and some have no specific limit. If your market is not covered above, ask the national standards body or your customs broker, and describe the requirement in your purchase order once confirmed.
What this means for your order
- State the flush volume, full and reduced, for each model and market on the purchase order.
- Ask for flush test reports at that exact volume, not at a higher setting.
- Check that the cistern fittings are factory-set to that volume and marked where the rules require it.
- Keep markets separate. A model set for 6 litres cannot simply be relabelled for a 1.28 gallon market.
Next step
If you sell into more than one market, we check each model's test report and cistern setting against the rule you name, and confirm them at inspection. Book a free sourcing review.