Table 1. A cycle refers to the concentration of water dissolved solids in the cooling tower water divided by the same dissolved solids in the makeup water. For example, suppose a tower water conductivity of 1,000 and makeup water conductivity of 200. Divide 1,000 by 200, which equals five cycles.

You can't imagine how much fresh water can be saved throughout the United States today with cooling tower water systems -- we all should be actively involved in water conservation to help reduce the drought impact on our drinking water supplies. Evaporative cooling water systems offer this opportunity in two ways: first, by reducing fresh water requirements by using less water and second, by utilizing "used" waters in place of fresh waters. In this column, I will write about conserving fresh water. My next column will deal with how to use "used" waters in cooling water systems.

It is estimated that there are more than 500,000 individual evaporative cooling water systems (cooling towers and evaporative condensers) in the United States. They range from circulating as much as 600,000 gal/min to as little as 50 gal/min. These 500,000 evaporative cooling water systems are estimated to currently utilize considerable amounts of fresh water (table 1).

It is likely with almost any makeup water quality and the newest water treatment chemical technology that these cooling water systems can operate at least to six cycles. This would result in the water savings shown in table 2. A potential of even greater water savings can occur by going to 10 cycles or higher. The potential water savings by going from three to six cycles is 1,576.8 billion gal per year -- this is almost 1.6 trillion gal per year! As the average household utilizes about 500 gal per day, this water savings could supply almost 13 million households.

Table 2. Increasing from three to six cycles of concentration would result in considerable fresh water savings.

At least two questions come up: Why are we not doing this today, and what would it take to accomplish this water savings?

First, it is being done at some large cooling tower users such as utility power stations, petroleum refineries and chemical plants, and even in some HVAC air conditioning systems, particularly where water is "short," water costs are high, or where the facility personnel have implemented water conservation to reduce the costs of water and water treatment chemicals. However, many medium and smaller -- plus even some large evaporative -- cooling water users still are not optimizing their water usage for many reasons. We know that there are systems operating at two or two-and-a-half cycles, others at three to five cycles, and some that can easily go to eight, even to 10 or higher cycles.

Many are not going to higher cycles due to a lack of knowledge that it is possible with today's water treatment technology and an understanding as to the magnitude of potential savings.

So what does it take to obtain these savings? Just do it! There are usually few costs, and the payback is in months rather than years. Let's help save our fresh water rather than waste it -- and let's start now!