Maintaining your targeted mash temperature, by sparging with hot water, is crucial for reducing lautering viscosity or having slowed runoff rates. It will also help maximize your extract recovery. Cold water also absorbs O2 more readily, allowing increased amounts of oxygen in your mash bed, causing further processing problems carried into the finished product.
Try cold water out. You may prove this theory wrong. Are there any other alternatives to storing hot water in your brewery? A fermenter perhaps, or another vessel?
Director of Brewing
Glenwood Canyon Brewing Co.
Glenwood Springs, Colorado