This topic is a double-edged sword that has two-tales ... I'll explain my interpretation of the two areas, and let you judge (or experiment) for yourself.On one hand
, many fellow corrosion collegues have proven that reverse osmosis water (less than 0.01 Total Dissolved Solids, ppmv) is almost non-corrosive because of the very low TDS value (there are virtually no chlorides/sulphates etc which provide conductivity to promote corrosion). On the other hand, the biologist in me says to never use reverse osmosis water on any life form. I do not remember the original surgeon, but the story goes something like this. A surgeon who performed operations removing problems from various internal organs originally used reverse osmosis since it is pure (this is absolutely true) and contained little to no infectious agents (microorganisms). The problem that did occur, was that when reverse osmosis water was being used on the tissues, the osmotic pressure would increase (regular tissue osmosis) causing the tissue that was being operated on, to swell and burst. The reverse osmosis water would be absorbed by the cells and become so large that the membrane would rupture. Once the reverse osmosis water was determined to be the problem, inorganic salts were added in small concentration to prevent cell burting from occuring during operations.
Similiarly, this may occur to your plant, you may be bursting the cell tissues. Granted, cellulose fibers (in plants) are usually much stronger than lipid layers (in humans), and water is no longer 'reverse osmosis' water once it touches the soil and absorbs nutrients/salts/etc.
Reverse osmosis water tends to have a lower pH (approximately 6 or so), and pH values below 7.5 tend to be more corrosive.On the other hand
, the regular salt concentration of tap water (lets say 140 ppmv TDS) contains many salts including sodium chloride and chlorine gas. This salt content increases the liquids conductivity and forms a conductive cell (similiar to a battery in your car, but only producing very small voltages and current) that cause the different metals in brass to corrode. In industrial water plants, calcium carbonate is added to form a hard protective coating to prevent the iron piping from direct contact with the water and salts, thus lowering corrosion. At this concentration of TDS, most cell membranes tend to remain stable, and not burst in the situation previously described with reverse osmosis water. Tap water usually has a pH between 7.5 and 8.0 (less corrosive), but does have about 2 ppm of free chlorine gas, which is quite harmful to microorganisms, which help create good soil for plants.
After all of this, I would recommend changing to plastic misting nozzles.
I hope this helps,
Eugene Dakin Ph.D., P.Chem.