Softner installing issue

I've installed numerous water softners. Most were replacement some new. All installs had a loop. I've just purchased a home without softner and ordered a system to install. Well I've just discovered that my home does not have a water softner loop for me to tie into. My question is, can I use the supply line for my water heater? Cutting into so that the water goes through softner before going to water heater? Everything I've found says I must use a loop. Any one have some insight?