Watering in the cold

Good morning, I was just finishing up poultry chores and headed into the hoop house to water when I realized I forgot to fill my jugs last night. How cold is really too cold for the water to be on my seedlings? Until now I’ve used gallon jugs of room temperature water while the weather is still cold here (45 F high today with an overnight of 29). My space is heated with a thermocouple dependant heater so it never goes below about 36. How warm does it need to be before I can switch to the hose? This time of year our water is chilly but not icy cold, probably about 45-50? degrees. (My beloved children broke the last of my thermometers). Thanks everyone, it takes a lot of trips back to the house to water 32 trays of seedlings.  

While I don't have a greenhouse I do have a method of mine that possibly you can adapt. When there's no freezing temps I leave my hose stretched out to the garden. The sun heats up the water in the hose. At this time of year we need to heat up the soil. So, I mist my seed beds with the warmer water. When it starts to cool I quit watering. Possibly you can leave your hose up high in the greenhouse so it warms up some. Later in the year I've always avoided using hot hose water as it's too hot.

I have well water which I've always assumed was at 55° F. It does get changed by what's in the hose/pipes and what's in the pump tank.