Total Water Demand

Water, water usage and consumption, and water quality. Perhaps the most essential and most misunderstood ingredient in the car washing business. Start with day one of the planning stages of building a new car care facility.  This fictional car wash facility is not an actual location, but rather a combination of the many different applications and locations.  Any similarities are coincidental.

First, several items must be certain:

- Proper zoning is approved.

- Property is under contract and pending final water and sewer approval.

- Traffic and all other business considerations are go!

Keep in mind we are focusing on water and water treatment only.  If specific items are not mentioned, they are not essential to the understanding required for water and water quality.

The model for use in this theoretical car wash facility is a 100-foot express conveyor. There will be both friction and high-pressure applications.  There will be a final rinse of spot-free water and an attached tunnel layout.  The objective is to reduce fresh water usage with an eighty percent water reclaim system.

Once it is proven that the facility can operate at 80% efficiency, the owner will be able to petition for a reduced city water meter and tap fee.  The facility will be using less fresh water and less water will be going to the sewer.  This allows the owner to ask for a reduced sewer tap fee.  Typically by reducing water demand, savings on both tap fees are seen. Tap fees are also known as impact fees.  The city speculates that high water demands increase the wear and tear on the city’s water treatment plant and water lines, as well as, sewer and sewer treatment plant.  Typically, there are formulas that help determine what additional costs from the car wash demand the city can expect.

One of the first items to be acquired from the city is the daily water test result.  Most municipalities test the water that is processed everyday.  This test should be made available.  The test may contain the results of  over 100 different tests that are preformed.  The results can be overwhelming. Only a couple of items are of interest.  Water hardness in grain per gallon or parts per million (ppm), chlorine levels, pH of the water, iron if any, Total Dissolved Solids (TDS) in a ppm scale.

Let’s be sure to mention,  water problems should be addressed at this time. Replacing the flapper in toilet holding tank every 6 months because of high chlorine levels in the water supply.  Hydrogen sulfide (sulfur), sending off a rotten egg smell. Replacing  copper pipes every couple of years due to small pinhole leaks that just pop up. All of these are just small examples that the consumer may be aware of in your city.  Share this information with your water expert.

For example, if the water test from the city is:  Water Hardness of 14 grains, Chlorine level 1.0 ppm, Iron 0 ppm, pH 7.5, TDS of 350 ppm.  No hydrogen sulfite.

GLOSSARY OF WATER TERMS:

Water hardness; hard water, is the level of calcium and magnesium in the water supply.  Hard water is measured in grains per gallon (grains) or Parts per Million (ppm), one grain of hardness is equal to 17.1 ppm.  1.0 to 3.5 grain in the water supply is considered slightly hard, 3.5 to 7.0 in the water supply is considered moderately hard, 7.0 to 10.5 is considered hard water and 10.5 and higher is considered very hard.

Chlorine levels; chlorine levels are adjusted by the water supplier.  Chlorine is used to disinfect the water as is travels through the water mains throughout the city.  Chlorine is removed from water supplies that feed Reverse Osmosis (RO) units.  Chlorine will damage the material of the membrane that purifies the water.

PH levels; PH is a way of measuring the alkalinity and acidity of the water supply.  A low pH number (0.0) means the water supply is more acid.  A high pH number (14.0) means the water is more alkaline.  The scale runs from 0 to 14.  With a pH of 7, the water is considered neutral.  Both sides equal themselves out.  Most city water suppliers like to operate at a slightly high pH.  This allows the alkalinity to scale the city water mains.  This scale is a small coating that will protect the water from decaying the water mains.

Total Dissolved Solids; (TDS) is a measurement of the ions that are dissolved in the water supply.  Another way to look at this is when a water droplet evaporates; the water spot left is the dissolved solid.  The naked eye cannot see water spots when the TDS levels are 50 ppm or less after filtration.

Parts Per Million; (ppm) and Milligrams Per Liter (mg/L) are two different terms that are considered the same scale.

Managing water demand is the bottom-line. The stage is set. Is it set correctly? The equipment layout of the tunnel is set.  This means total water volume is set as well. Peak day of operation must also be considered.  This article is going  with a peak demand of 800 cars per day (cpd), and an average of 5,000 cars per month (cpm). The car wash will be opened 12 hours a day.

Total water demand will be calculated in gallons per minute (gpm).  First address the total water demand, and break down the different water supplies that will be used; water reclaim, city hard, city soft, concentrate and spot-free.

The next step is to break down of the different water supplies that are planned and where use them.  Keep in mind the goal is to reduce the fresh water consumption, which will reduce water and sewer tap fees.

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