When I leave for multiple weeks I leave an automatic water pump to water some of my more needy plants. When I returned, I noticed there were white patches on the water pump, as well as on the surface of the water in the tank I used.

This had happened the previous time I set up the automatic water pump, which stayed in the water for about a month, even though it took much less time for the issue to develop this time and the patches are much more prominent.

Last time I encountered this, I tried washing the pump with hot water, but it doesn't seem to have prevented the issue occurring again.

Once removed from the water, the patches on the water pump became dry and broke apart.

I am unsure whether the presence of this substance in the water has affected my plants negatively. The two plants being watered from the tank are a Spider Plant and a Dracaena Massangeana. While the leaves of both plants look droopy and there is some tip burn (which may or may not have been there before), I haven't noticed other symptoms.

  • What are these white spots in the water and on the pump?
  • Should I throw away the pump, as the substance may have spread all throughout it?


white spots on pump white spots on water surface

  • Looks like salts dissolved in the water have dried. If there are pin point leaks where you see the white stuff that would be it
    – kevinskio
    Feb 22, 2018 at 19:03
  • It's hard luck .. Well at least hard water! Feb 22, 2018 at 20:16
  • If I understand correctly this means it’s not some kind of mold or organism growing in the water due to it being stagnant then. What leaves me wondering is why did it only happen this way the last time I used it (it happened the previous time too, but as far as I could tel the “blobs” only started developing after I left the pump in the water for too long. I don’t think it was running at that time however, so they wouldn’t have a chance to form as you described. I guess one way to test that would be to just submerge the pump again and see if the growth occurs autonomously.
    – kettlepot
    Feb 22, 2018 at 23:04
  • Check the inside of your kettle. Feb 23, 2018 at 0:33
  • Kevinsky is right. This is salt buildup from your tap water; fluoride and all the other industrial waste products that are dumped in our drinking water (completely true, I am very sane and serious) never been shown to to do a single good thing for our teeth. It is not mold or any kind of life form. It is chemical waste that would normally cost lots of money to dispose of correctly so someone got this idea to tell people fluoride was good for teeth and now all cities have to comply and have this stuff disposed of in our drinking water. Aluminum and phosphate industrial waste.
    – stormy
    Feb 23, 2018 at 1:48

2 Answers 2


Very likely to be hard water deposits , certainly not mold. That is; Ca, Mg, etc carbonates. Apparently that is a galvanized steel pipe , if it were corroding the deposits would have some degree of red color . Salts would corrode the zinc ( white) then the steel ( red) , because that is not happening we can say it is Ca , Mg CO3 , and not "salts". I doubt very much that is anything the city is putting in , although about the first element they might put in would be Al ( to clarify ). Your only potential problem is soil may become alkaline , check the pH.


Is this a recirculating system? If so you may have salts from fertilizer in addition to those in tap water. Try immersing the pump in vinegar (unless the instructions tell you not to) - if the patches on the pump disappear then you have both an answer and a temporary solution to the problem. Does it rain where you live? If so, fill the tank with rain water, which usually contains far fewer salts.

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