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Reservoir savoir faire

October 11, 2010
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With the cost of municipal water having doubled or tripled in most places over the last three years, the search for alternative sources of water has arrived. Many water providers are getting serious about loss prevention and inefficient practices.

For instance, new technology offers water providers instant pay back for meter replacement along with lower operating costs for the town and city utilities that choose to implement them. Water providers can now monitor meters from remote locations and keep tabs on water usage much more closely. Leaks and backflow issues that used to go unnoticed on your bill can now be easily discovered and charged for accordingly.

Size up your water line, meter and rate
Using a reservoir to create a buffer supply of water can reduce the size of the water line needed to operate your site. Depending on the type of washing equipment and consumption during operation, there is usually sufficient time between washes for the reservoir to replenish the amount of water used to supply the demand.

The size of the incoming water service line and meter will determine the amount of upfront fees and rate of monthly charges. It is always advisable to check with your utility provider before you build to get an idea of what the cost of water and sewer will be before building your site. It may also benefit you to ask if any rate changes are looming in the near future or if there is a schedule of rate increases already planned for your location.

Taking a creative approach to fulfilling your water needs prior to construction or instituting water saving methods at an existing site could be worth thousands of dollars to you.

Save money, save water pressure
Saving money on the initial water service is not the only benefit of using a reservoir in a carwash site. It also solves potential low-pressure problems. Low water pressure after the backflow valve is becoming a common issue all across the country. By utilizing a pump to pressurize the stored water for the specific demand of the site, correct volume and pressure will be guaranteed, eliminating times of insufficient flow at the site. By using technology available, one can obtain this goal quite easily.

Using a reservoir allows the introduction of water from nontraditional options. For example, rain water harvest is certainly catching on in many areas across the globe. Capturing rain water from sources such as roof drains, canopies, and any clean runoff can offer not only a supplement to the reservoir, but is also an excellent marketing tool in our green conscious society.

Ultrafiltration (UF) is another viable option for a supplemental water source. The UF membrane system will filter the spent wash water to one hundredth of a micron below virus and bacteria levels. The high-quality effluent produced by the membrane system is an excellent supplement for any type of collection system. The membrane water produced is of such quality that one can blend with fresh water at a 50 percent ratio and feed it into a reverse osmosis (RO) system to produce spot free water.

Membrane systems can also be an effective solution for sites that have discharge restrictions on wastewater. The EPA is currently prioritizing a standards program to reduce nutrient pollution. Future regulations are expected to be more restrictive. The days are numbered for the many sites that bypass the sanitary sewer and discharge to the environment.

High pressure water
The following example will illustrate how to use a reservoir tank at a location with limited fresh water for a high pressure automatic wash system.

The location has an existing fresh water city feed line to the equipment room. The cost to increase the size of the city line is prohibitive in two ways:

1. The cost of concrete removal and replacement is costly at a minimum.

2. The fees involved with changing the service line and meter would be over three times the amount of the construction expense.

The new high pressure automatic uses 32 gallons of water for the average wash. The owner calculates that he will wash eight cars per hour with water usage at approximately 300 gallons per hour. The existing 3/4” water line will produce 6-8 gallons per minute; however, the pump on the wash equipment consumes about 30 gallons per minute.

Plumbing the existing line to an 800-gallon reservoir tank with an electric valve and float switch will help to fill, maintain, and shut off the freshwater line to the reservoir.

The city water flow will average seven gallons per minute for 60 minutes giving a total of 420 gallons per hour city feed. The pumping station can consume a maximum of 300 gallons allowing a buffer of 120 gallons.

The most the pump station will lower the volume in the tank is the total amount of cars washed times 32 gallons. During the 3-4 minute wash cycle the city water will replace 21-28 gallons in the reservoir, meaning we have used 10 gallons from the storage tank. Operating at a deficit of 10 gallons per wash the 800 gallon reservoir tank could supply water to wash 80 cars in a 10-hour period.

Low volume solution
When using a reservoir system to solve a low volume or low pressure situation, start by calculating how much fresh water you have to work with. The following questions will be instrumental in your determination of reservoir sizing:

• What type of wash equipment is being utilized?

• What is the consumption of water per vehicle? (A realistic estimate of cars that can be washed per hour.)

• How many hours of operation per day?

Calculate the difference between the amount of water being used per hour and the amount of water available per hour. This will determine how large your reservoir will need to be and if the reservoir can be replenished during slow and non operating hours. Please keep in mind that the reservoir can be supplemented by other sources. (See chart in sidebar)

Know about RO spot free systems
For sites incorporating RO spot free systems, the municipal fresh water line will need to be connected to the RO unit directly. The RO water will be sent to one tank and the RO reject water will be sent to the reservoir. A “T” plumbed in the fresh water line before the RO unit will be sent to the reservoir for supplemental water for the reservoir tank.

By using a reservoir in the wash process, you can provide constant volume and pressure to the wash equipment without relying on the ups and downs of municipally supplied water, or purchasing a larger service at prohibitive costs to you.

Jim Keller is the president of Con-Serv Manufacturing, a manufacturer of the water saving equipment, based in Lakeland, FL. For more information, visit or call 800-868-9888.

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