Standard gravity tank toilets are the most common type of toilet installed on accommodation premises, and do not require high water system pressure. Of these, button-operated flap valve cisterns offer the lowest installation costs, but are vulnerable to leakage from small particles preventing a seal and worn rubber seals (Environment Agency, 2007). Leaks occur in up to 20 % of installations, and can waste considerably more water than is used in actual flushing, but are difficult to detect. Regular inspection of toilets, including new low-flush toilets, is therefore important.
In addition, flap valve cisterns allow refill water to flow through the cistern during the flushing, increasing flush volumes by up to 17 % (Environmental Agency, 2007). Cisterns containing siphon-controlled outflows are more expensive to buy and result in slower cistern refilling that can in some cases restrict their practicality in commercial settings, but result in a considerably reduced leakage rate. Low and dual flush toilets with siphons are available (Green Building Store, 2009), and may prove cost-effective when lower leakage rates are considered over the installed lifetime.
Cistern displacement devices can be inserted into cisterns to reduce water volume, or the float-arm may be adjusted to lower the fill level. Cistern displacement devices may be purchased, or improvised from e.g. bags of pebbles or plastic bottles full of water. When inserting cistern displacement devices, it is important:
Dual flush toilets should be clearly labelled so that guests know how to operate the low flush (e.g. which button to press). Reassurance should be sought from the relevant authorities that the local sewer system is compatible with low-flush toilets: i.e. that installing such toilets will not significantly increase the risk of blockages (EC, 2009).
Valve-operated flush toilets are more expensive to install than gravity-tank toilets, but do not require any refill time and are therefore appropriate where the frequency of use is high (for example common toilet areas). They cannot be easily retrofitted and should therefore be specified during construction or renovation. Valve-operated toilets require a system pressure of at least 1.8 bar, and should be fitted to bowls designed for shorter, higher pressure flushes (EC, 2009). Valves are fitted directly to the water supply system and are manually adjusted to produce the correct flush volume at the location-specific pressure, resulting in a low volume when correctly adjusted (periodic checking required).
Pressurized tank toilets are also more expensive than gravity-tank systems, and have comparable refill times, produce a more effective flush and enable lower flush volumes. They comprise a sealed plastic tank containing pressurized air behind a diaphragm that is compressed by water from the pressurized supply system (at least 1.8 bar required). Pressurized tanks can be retrofitted, but are easier to install during construction or renovation.
In all cases, it is important that flush effectiveness be maintained otherwise water savings can be negated or even reversed by repeated flushing. For pressurized flushes, it may be necessary to change the toilet bowl to achieve best results.