The simple answer is the total volume of water used in the entire brewing process with respect to the finished volume of beer produced.
How is it calculated? If you keep track of your water usage, it’s pretty easy to calculate. During the brewing process, water is not only used for the beer itself, but also for chilling and cleaning. For example, in my brewing process for a typical 5 gallon batch, I use on average 25 gallons of water from grain to glass, resulting in a water to beer ratio of 5:1. A detailed calculation is seen below:
Total Brewing Water Calculation for 5 Gallons of Beer
Wort: 7 gallons (5 gallons of wort, 1 gallon in grain absorption, 1 gallon in boil off)
Chilling: 8 gallons (5 gallons for water bath, 3 gallons for ice bath)
Cleaning: 10 gallons (5 gallons each of PBW & StarSan re-used for both keg and fermenter)
Water Usage Total: 25 gallons
Batch Total: 5 gallons
Final water to beer ratio: 5:1
Why is this important? Cost (if you’re a big time commercial brewer) and environmental impact. Indeed, water is arguably the most important asset in the brewing process (if not the entire world!). To give a frame of reference, as reported by craftbrewingbusiness.com, the average commercial brewery uses a water to beer ratio of 7:1 (I don’t feel so bad anymore). More importantly, craft breweries are lowering their water to beer ratio on a year to year basis, some reaching 3:1 (maybe I can do better?). Even the big boys are improving their water usage. For example, SABMiller (Miller Lite, Blue Moon, etc.) have reduced their water usage from 4.5 in 2009 to 3.7 in 2013.
What can homebrewers do? In my opinion (standing on a soapbox now), I would focus on the three R’s: Reduce, Reuse, Recycle. In most cases, the three 3 R’s are most easily applied to chilling and cleaning.
Reduce: If you are daring, amazingly, there are some no water chilling techniques homebrewers routinely use. Aussie homebrewers (inventers of BIAB) use no chill methods. Winter-bound northerners use cold outdoor temps for no water chilling. Not daring, no problem, technology can help. The easiest method for more efficient cooling would be investing in a wort chiller. On the cleaning front, most cleaners and sanitizes can be reused. For example, I reuse StarSan for a few batches, until its pH reaches near 3. Also, when cleaning with PBW, I use it on lightly soiled brewing equipment first, then use it on more heavily soiled items, until it is no longer effective.
Reuse: The next best thing! There are many options here. Best advice: be creative! My favorite is reusing chilling water for the garden (my apartment balcony garden). Important note here, chilling water is hot, so it is necessary to collect it first, and let it cool down, then use on the thirsty plants.
Recycle: When the above options don’t apply, the best option is to make sure the water you are using goes back to water treatment plant (i.e. down the drain) rather than dumping outside (garden aside). Water down the drain might be a waste, but at least it is conserved. Water outside evaporates, and moves outside of your locality (hence water restrictions during the hot summer months). Drought-ridden people of California and Texas know all too well about this. Not fun. (Stepping off of soapbox now).
What do you do with your unused brewing water? Are you more efficient than commercial brewers? Share your experiences in the comment section below! Cheers, and happy brewing!