water mass balance Cirencester, 20 October 2009 Carole Bond Envirowise Advisor ADVICE LINE

Overview background overview points of note practical exercise: the department store ADVICE LINE

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Mass balance Demonstrates numerically where water enters and leaves your business Serves as a management tool Helps you to understand and manage water and effluent efficiently Identifies areas with greatest cost saving potential Assists with leak detection

Mass balance

What goes in must come out somewhere

Water Balance-Industrial Site ADVICE LINE

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Example Water Balance-Hotel

points to note ADVICE LINE

Consider inputs The incoming water supplied to a site can include a variety of potential sources: town mains supply underground sources (abstraction) surface water or rain water process water, recirculation` or effluent recycling To construct an accurate water balance, you need to take into account all of these potential sources. ADVICE LINE

Mains water supply There are a few things to consider if you monitor your usage using your water bills: your site may have more than one supply, especially if you have a large site each of the supplies is likely to be billed separately This information can be obtained from the water company or from the person or department responsible for paying your bills. ADVICE LINE

Groundwater abstraction Some of your sites may have a licence to abstract groundwater at one or more points. These include annual volumetric limits and limitations on what the water can be used for. Abstractions are metered to ensure that they comply with the licence. Consider how the water is being used and where it goes; for example, the abstraction may be used for cooling and returned in a closed loop system and, therefore, the net usage would be zero.

Water in raw materials Raw material product specifications should detail their water content. Multiply these by the volume of the material used to ascertain the volume of water input from this source. As this would involve calculations across your whole raw material range, it's not worth considering unless your raw materials introduce a substantial amount of water into the process; for example, dried milk, where a lot of liquid is evaporated off. ADVICE LINE

Consider outputs The outgoing water from a site can be released via a number of routes which can include: discharge to sewer, surface water or sea via evaporation or in the product waste (in liquid wastes or effluent sludge cake) leaks All have to be accounted for to ensure that the water balance is accurate. The total should match the incoming water to the site. ADVICE LINE

Discharge to the sewer This was covered in this morning’s presentation. Your bills will detail: your consent number trade effluent volume (normally a set percentage of the incoming water supplied) amount used for domestic purposes (toilets, showers, kitchen areas etc.) ADVICE LINE

Discharge to surface water or sea Discharge to waterways or the sea tend to require pre-treatment in an on-site effluent treatment plant. Normally, the effluent treatment plant would provide a measurement of the volume of liquid treated and, therefore, how much is discharged. A variation is where water is used for cooling and returned directly to the water source in an enclosed system, after the heat has been taken back out.

Evaporation Almost all sites will have some form of evaporative loss from processes. These losses can be from: cooling towers; heat treatment within the process; combined heat and power plants, boilers and other energy raising equipment These losses may be very difficult to quantify. ADVICE LINE

Water balance doesn’t add up? If there are still discrepancies in the water balance then this will be down to gaps in the data. These gaps can be: not all incoming water sources accounted for not all outgoing discharges accounted for leakage on-site miscalculations with regards water in product, evaporation, water in waste streams etc. inaccurate meter readings

Identifying leaks The simplest way to identify an on-site leak is to monitor the meter when the site is shutdown and no water is being used. If the meter is still logging water consumption then there is a leak on-site. Ensure that all urinal controls in gents’ toilets are shut-off, as they often run over weekends and flush several times an hour. Also, boiler plant and cooling towers may be in operation over the weekend so it should be checked that these are off, or if they are on, how much water they are likely to use. ADVICE LINE

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