At what low temperture would you think watering "shocks" the plant?? Room temperture varies in my grow room!! The water on my bottom shelf is about 64 degrees the middle shelf 72, upper shelf about 80, I always use the upper shelf water and rotate upwards, as it warms I guess any crap the city may add evaporates, or it's suppose to. I've never had it tested except PH. with my room temps around 78,at the top of the canopy, they seem to like there water at around the same. In my opinion anything under 72 may shock them.