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Calculating Urinal Water Consumption
Gentworks has designed a Microsoft Excel spreadsheet to help you calculate how much water is used for flushing urinals. To load this, please click the icon below. Note that the spreadsheet will open in a separate window so you may need to give permission for a 'pop-up', should your browsing software request it. If you have any comments about the spreadsheet or would like some advice, please email support@gentworks.co.uk or call 0845 202 4535.
The most accurate way to assess the amount of water being used to flush urinals is to fit a water meter on the pipe that supplies water to the urinal cistern(s). In the absence of a water meter, a reasonable assessment can be made by multiplying the capacity of each cistern by the number of flushes that occur over a 'normal working week'. Of course, such an exercise would be very time consuming unless an electronic flush controller with an audit facility is fitted, and these are rare. Counting flushes by sitting in the washroom all day for 7 days is not a realistic or attractive option for most people.
Gentworks has surveyed several thousand washrooms over the last 7 years. Based upon our experience, our spreadsheet incorporates some assumptions for the frequency of flushing for urinals with and without flush controllers. For ease of use, the spreadsheet assumptions are generic, but the cells can be overwritten with more accurate data gathered from your washrooms.
In the absence of a water meter or sophisticated flush controller, the best way to assess ‘flush frequency’ is to count the number of flushes that occur in 1 hour. If an hour cannot be spared for this exercise, then time the period between one the beginning of one flush starting and the next. Use this reading to calculate how many flushes an hour this indicates. In washrooms where no flush controller is fitted, the result should be reasonably representative of every hour, every day.
Flush controllers are fitted in many washrooms and are now a requirement of water regulations. During site visits, Gentworks engineers find that around 20% of flush controllers installed are not operating correctly or have been disabled. Therefore, the presence of a"box on the wall" does not necessarily indicate that flushing is truly being controlled. Generally, if you can hear water flowing into the cistern for longer than 10 minutes, even though nobody is activating the controller via the sensor or other means, then the likelihood is that the controller is not working correctly, if at all. Notable exceptions are the Cistermiser EIRC and IRC2 controllers which are designed to fill the cistern for a period of 30 minutes after sensor activation.
If a flush controller is working correctly, it will be saving a great deal of water. The downside is that this can mean maintenance costs are higher because blockages can be more frequent. A urinal that flushes every 5 minutes is umlikely to block, whereas long periods between flushes allows limescale, uric acid salts and debris to build up in the waste pipes. Therefore a balance between water usage and maintenance expenditure needs to be achieved. Unless waterless or low-flushing systems are installed (see www.waterlessurinals.co.uk), Gentworks recommends that urinals should be flushed within 20 minutes of use and every 12 hours when not in use.
Most models of sensor flush controllers activate the flush after a given number of minutes has elapsed following use of the urinals. Most models have variable settings to allow between 1 and 6 flushes per hour. A reasonable assumption is that urinals with sensor controllers will flush every 20 minutes during 'working hours'.
If the sensor is not triggered for a long period (e.g. overnight or at weekends) then a 'hygiene' or 'janitorial' flush should occur after a preset number of hours, usually 6, 12 or 24 hours depending on the model of controller. However, on many sites, it would be incorrect to assume that the sensor is not activated at all outside of 'working hours'. Late night workers, cleaners and security personnel could enter the washroom so the typical interval between flushes outside of working hours is around 4 hours.
One of the most instantly recognisable flush controllers is the Cistermiser hydraulic urinal valve. These units react to a reduction in pressure within the water supply pipe causes by someone using water from the cold tap to wash their hands, for example. The valve will then open for a short period and let a small amount of water into the cistern. In most cases, many activations are required before the cistern fills and flushes. It is notoriously difficult to estimate the frequency of flushing as there are so many variables, but an assumption of 2 flushes per hour during 'working hours' and every 8 hours outside of working hours is as good as any. This type of controller remains popular but Gentworks engineers find them to be the type most likely to be no longer functioning, often due to age or lack of maintenance.
Cistermiser IRC2 flush controllers work a little differently to most. Once triggered, the sensor will open the valve for a set period of 30 minutes. Depending on the speed of water flow, this will typically result in 1 or 2 flushes during that period. Whilst this may result in a similar flush frequency to other PIR sensor controllers, it is also possible that more flushes occur.
Although relatively rare, there are models of flush controller that activate flushes at preset intervals (e.g. every 30 minutes) or are set to flush every 15 minutes between certain hours (e.g. 08:00 to 19:00). The most well known brand in the UK is Barflo, although we understand that this is no longer in production. Assessing the frequency of flushing should simply be a matter of viewing the timer settings. However, in the case of a Barflo controller, it is worth checking how often the urinals are flushed during a 30 minute period. Depending on the calibration, it may flush as many as 4 times during half an hour.
If you wish to dramatically reducing urinal water usage without increasing maintenance costs, you should consider converting to waterless or low-flushing (once every 4 hours). For details, please go to www.waterlessurinals.co.uk .
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