Helton Construction can provide the permitting and installation for both well and septic that the State of Colorado requires. If a property is not served by a municipal sewer system, you'll need a septic system. If you know that municipal water is available on the property, chances are (but, not always) the property is also served by a sewer system.
If the property relies on a well for water, or if it's outside of city limits in a rural area, you'll probably need to install a septic system (which handles the waste water from your property only). All land in Colorado is subject to state and local laws governing the installation and maintenance of septic systems.