low-flow-aeratorIn one of my last posts on water conservation I mentioned significant savings several times, but never got a chance to calculate some of those potential savings. So, here are a few of the numbers…in somewhat unscientific fashion…

First, there is not a lot of data on water use in restaurants, and the data that is available is not very detailed and varies quite a bit. What is available shows use anywhere from 900 gallons per day to well over 7000 gallons per day so its hard to say what an average would be. In addition, most of the numbers that are available tend to just give rounded numbers for an entire restaurant’s use rather than broken down to individual uses like dishwashing, hand sinks, etc. So, I’ll try to make an estimation based on general use rather than being based on total use.

Lets take the aerator idea as an example. Say a restaurant has a number of faucets all with 2.2 gallon per minute aerators installed. Over the course of the day, all the sink uses (minus the dish sink and dishwasher) add up to two hours. So every time someone washed their hands, rinsed some vegetables, filled a glass of water, or a mop bucket the total running time of the faucets added up to two hours. This is a fairly conservative estimate based on the water use data, and also assumes the restaurant did not thaw frozen product under running water, which can add over two hours of use alone.

Total water usage and cost at this establishment would then be:

120 (minutes) * 2.2 gpm = 264 gallons / 1000 = .264 kgal * $7[1] = $1.85 per day

$1.85 * 360 days a year = $666.00 per year for faucet use.

.264 kg * 360 = 95.04 kgal per year

Now lets assume they installed 1.0 gpm aerators in all the faucets. As I mentioned in the previous post, this would reduce their water consumption by 55%. However, because a certain percentage of the water use is for drinking or recipes, or other uses where an absolute amount of water is required regardless of the aerator we cannot assume a straight 55% reduction in water consumption. Based on data from restaurant water consumption reports, lets assume 35%[2] of use is non-absolute amounts. Meaning handwashing, rinsing produce and any other water use that does not need a set amount like a glass of water would. I’ll use time as the divisible factor, and 2.2 gpm for the 57% of use that is for absolute needs rather than calculate it at 1.0 gpm, and multiply it by 2.2 to get what the actual use would be.

The water use and cost with 1.0 gpm aerators would then be:

78 (minutes) * 2.2 gpm = 171.6 gallons / 1000 = .172 kgal * $7 = $1.20 per day

42 (35% of total) * 1.0 gpm = 42 gallons / 1000 = .042 kgal * $7 = $.29 per day

(1.20 + .29) * 360 days = $536.40 / year

(.172 kgal + .042 kgal) * 360 = 77.04 kgal / year

$666.00 (cost with 2.2 gpm aerators) – $536.40 (cost with 1.0 aerators) = $129.60 savings per year

So, $130 a year may not seem like a “significant” savings, but considering the amount invested (roughly $2 per aerator) the payback is huge. That is about a one-month payback period if seven aerators were replaced with no maintenance or updating needed ever. Unlike other efficiency measures, faucet aerators are an install and forget it fix. There is no other measure that is as cost effective. Basically, regardless of how one calculates the savings, or the restaurant’s daily water use low-flow aerators are a simple, low cost solution that should be used in every establishment.

[1] http://www.reuters.com/article/pressRelease/idUS163067+24-Sep-2008+MW20080924

[2] American Water Works Association Research Foundation, Commercial and Institutional End Uses of Water, DeOreo, William et. al., 2000


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2 Responses to “Calculating Water Savings”

  1. Faucet Aerator Guy Says:

    Great post, love that it is backed with a data / cost savings approach.

  2. Ramya Says:

    Hi, nice information, have you clearly explained the water usage. I can buy the faucet aeratorsfaucet aerators to my home and I can reduce the water wastage.

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