Warm Water For Winter Greenhouse Irrigation

[Millet]

I collect rain/snow water off of two large barns into one hundred 55-gallon open top drums.  At this time of year the collected water is quite cold, some mornings even a little ice. I  painted ten 3.5 gallon plastic pales black, which I fill with the rain water each morning, and set them inside the greenhouse flush against the inside south wall of the greenhouse to absorb the sun's light heating the water.  By noon on sunny days the water is 70 - 80-F. which I then use to water the 10 container tomatoes. citrus trees, pineapples and other plants.  This gives me 35 gallons of warm water every day.

[Citradia]

Good idea, Millet! That's a lot of free warm water!

[Vlad]

What is the temp in the greenhouse?

[Millet]

Vlad, the greenhouse temperature all depends on the day, and how sunny.  My greenhouse is at an elevation of 5,440-ft so the sunlight is quite strong. On a sunny day the temperature starts out about 45 to 50-F and  can eventually reach anywhere from 60 to 80-F

[Millet]

I conducted an experiment today.  I placed a pail of rain water that was collected from the 55-gallon drums outside, and moved it into the greenhouse, but in an area where it received no sunlight.  When the water was bought into the greenhouse this morning the water temperature was 38-F.  At 1:15-PM the black pails setting in the sun along the inside greenhouse south wall had a temperature of 74-F. and the pail that received no sunlight, but only some residual internal greenhouse heat was 57-F.

[brian]

I tested the tap water coming out of my greenhouse faucet as 55F.   Is this too low to apply directly to container trees?  The tree root temperate was around 50F after a cold night.  I realize that 70-80F water is probably ideal, but given that the water is already warmer than the container soil I would hope there is no problem applying it to my containers as-is.

[Daintree]

I use a 300 watt fish tank heater in my greenhouse pond in the winter, which I fill with our tap water, then filter.  Way more expensive than what Millet does, but much easier on my back! 
I heat the water to about 80 degrees, and my tropicals love it.  I only have to do that in the winter, since in the summer, it gets warm enough on its own.
However, I do plan on putting gutters on my greenhouse this spring to start collecting what little rain we get. 

Carolyn