I wonder if water hardness make any difference?

The So Cal town where I grew up had terrible water.  My dad had a well drilled on our property.  City water was so bad it was undrinkable, and most people had bottled water in their homes for drinking.  The church camp where my wife and I have volunteered had to put in a reverse osmosis system because there is so much iron in the water.

I'm wondering if the chemical content of the water makes any difference as to whether a wetting agent is needed?

Water hardness

Water hardness could make a difference.  In stating that plain water was used, I should have mentioned that our water is filtered.  A large part of our municipal water comes from the Colorado River and is very hard by the time it gets next to the ocean.

Water Hardness

Whether it’s hard water, high iron content, or high chlorine content, all these things can significantly impact the performance of your modeling efforts. More importantly those water problems are hell on your appliances and plumbing fixtures. Hard water and 125-150 percent increased natural gas are the two reasons I won’t buy a tankless water heater. Though I can’t speak to the efficiency of the misting sprayer I will say aside from mixing plaster use distilled water for your modeling endeavors. It’s cheap, even in today’s economy. I use it almost exclusively for my homemade wet palette. Distilled water makes thinning water based and water soluble paints a breeze. 

Re: Water Hardness

Our water system's published data shows hardness is: Average= 230 mg/L; Range= 151 - 292 mg/L.  That makes it "Hard", but not "Very Hard" (which starts at 300 mg/L).  No idea what data is after filtering.

SMR painting and decaling switched to using distilled water decades ago.  Wetted water continued for scenic use until the recent serendipity with the sprayer. 

It is more convenient to use faucet water for scenery, but distilled water would remove any concerns about hardness.  Certainly, only distilled water should be used for painting and decaling.