In one of my earlier columns, I pointed out that water conservation may be achieved by simply increasing the cycles of concentration. This has been made possible by the development of outstanding deposit control inhibitors -- those known as crystal modifiers.

Another method currently gaining popularity for water conservation is the use of "used" waters in place of fresh, often potable, waters. Used waters are any water that has been already used for other means and often is discharged. Below are some examples from external and internal sources that often are acceptable for evaporative cooling systems:

Enlarge this picture Some reclaim waters can be used without further treatment; others may require treatment. Reusing "used" water reduces fresh water use.

External Used Water Sources for Cooling Water Systems

• Treated municipal wastewater
  
• Mine drainage waters
  
• Industrial wastewaters
  
• Gray water
  
• Irrigation runoff

Internal Used Water Sources for Cooling Water Systems

• Boiler blowdown
  
• Oily or contaminated steam condensate
  
• Zeolite softener rinse water
  
• Demineralizer rinse water
  
• Air-handling coil condensate
  
• Reverse osmosis reject water
  
• Cooling tower blowdown
  
• Process waters
  
• Pump seal leakage

Some of these waters can be used without further treatment; others may require treatment in order to be utilized.

Reusing "used" water reduces fresh water use, making it available for potable purposes. Better yet, these used waters often are free or very low in cost to reach the evaporative cooling system.

Both small (left) and large (right) cooling towers can use used waters as a part of the cooling tower makeup water requirements. Reusing used waters in evaporative cooling water systems can save facilities money.

The water treatment program may require some modification to deal with any contaminants in the used waters. This depends upon the metallurgy and operating conditions of the cooling water equipment (i.e., cooling tower, heat exchangers, chillers, and piping).

A typical example of using used waters as part of the cooling system makeup water requirements and the impact on the final cooling system water quality is given in table 1.

Water conservation is greatly needed today. Reusing used waters in evaporative cooling water systems makes sense and also saves many dollars. Many industrial users such as utility power plants, petroleum refineries and chemical plants can switch to used waters and begin enjoying the benefits immediately.