How Make-up Water Can Affect a System

Water treatment starts with the water you put into a system. Whether the source is from a municipal drinking water system, a well, a river, or a lake, changes in the make-up water chemistry can occur that will affect a system. A particularly interesting water source is “gray water,” which is often a topic all to itself.

Although the chemistry of the water from municipal systems is usually very steady, there are a few areas, like Carlisle, PA, where I discovered the chemistry could change weekly. In fact, the hardness levels in a Carlisle area boiler house would fluctuate enough that you had to pay close attention to the softeners; otherwise, the outcome surely would have been short runs on the softeners and hardness excursions to the boilers.

Another example is a cogeneration plant in southern Pennsylvania, where the source water came from a lake that contained colloidal silica and needed to be monitored carefully. Left unchecked, the colloidal silica would have caused great problems with steam quality for this 1,200 psig boiler.

One other system of note was a cooling tower using a stabilized phosphate program where the phosphate levels started climbing out of control. The source water for this system was drinking water from the local lake. Due to the seasonal farm runoff, there was periodically 1 to 2 ppm of orthophosphate in the drinking water. At 10 cycles of concentration, that resulted in more than 15 ppm of orthophosphate without chemical feed. With more municipal systems adding orthophosphate as a corrosion inhibitor these days, this scenario is likely to happen much more frequently.

The concept to take away from all of this is the importance of understanding your make-up water sources. Some will stay rock steady―others can change rapidly. Changes in the make-up waters dictate changes in programs and economics of treatment. Kicking the chemical drums and looking at the log sheets may not be telling you the whole story.