We do not endorse any of the contractors you may find on these links below.
Call and get at least three estimates over the phone. Ask for an estimate for "time and materials not to exceed a certain dollar amount." If they will not give you an estimate over the phone, call someone else. If they state that they only service what they sell, then they are not a service oriented company.
Ask how many years they have been installing and servicing water softening systems.
Ask that they send out an experienced technician/installer.
Installing a system in a home that has been pre-plumbed or roughed-in should only take around 1.5 hours if the drain and electric are present at the rough-in. An experienced water softener installer should take up to 2 hours to replace an existing water softener. A typical basement installation should take up to 3 hours not including plumbing your outside faucets hard.
A whole house filter will take less time since it does not have a salt tank.
A reverse osmosis system will take about an hour to install under a kitchen sink and up to two hours if it is installed in the basement. If an ice maker line is run, this may take another 30 to 90 minutes by itself.