Can cactus distinguish between tap and rain water?

Factual Questions
1

I seem to notice more profuse blooming of cacti and succulents after a rain here in So Cal, it might just be my imagination but there always seems to be more profuse blooming all at the same time right after a rain. Is this possible?

2

It’s possible that the chlorine in tap water adversely affects the cactus. Also I assume that the cloudy skies that come with a rain might make it cooler. I don’t know if that would affect the cactus.

3

or the additional nitrogen in rainwater is beneficial:

http://www.startribune.com/lifestyle/homegarden/44463677.html

4

Your title question and your post question appear to be different.

It is quite possible that there is a greater profusion of blooms following a rain. I would speculate that is is possible that cacti have evolved to take advantage of rain. It is possible that the formation of blossoms is predicated on a reduced need to conserve water in desert conditions and that the presence of rain relaxes the “water hoarding” activity while redirecting the energy used to conserve water toward propagation.

Separately, rain water and tap water can have a lot of different features. As noted, chlorine and fluoride will not, generally, be present in rain water. Even if the tap water is based on a well with no industrial additives, it will generally have much higher concentrations of iron, calcium, lime, and other ingredients that leech into the water from the ground in which the aquifer is found. What affect any of those would have on the number of blooms or their duration I could not say.

5

What does tap water have to do with it? Are these all irrigated cacti?

Many plants that experience dry seasons or drought are programmed to bloom synchronously after rains. So there will be increased blooming after rain during a dry period.

Plants that are continuously watered may not receive the same cues. If they always have sufficient water, they may not bloom at the same time.

6

Agreed - Traditional wisdom for inducing bloom in potted cacti is to try to avoid watering for months (some say a year), then plunge the pot in water level with the soil surface, wait for bubbles to stop, lift out and drain - simulating the watering effect of heavy rain after an extended drought.