% Q0 D: d9 h& d: y$ W$ b7 nHot water has went through all your home's internal pipes whereas cold water comes "direct" from your local reservoir. Which should be pretty safe. 6 Y$ s4 b$ o' \1 Q: t H# n |' _# [, ^$ ^5 N
Beside,furnace hot water coil is made of metal. Some of it will come into the hot water.