Public utility services are organisations, public or private, that are formed with the intention of serving the basic needs of the public like electricity, gas, water, transport etc. Anything that has to do with serving the basic needs of the general public is considered a public utility company.
In general, it is agreed upon that public utility services be taken upon by the government, since private firms are normally profit-centric and their services will not be accessible to all classes of people. For this reason, private investors are generally discouraged from investing in the public utility sector, since they normally require large scale investment and would not work as a non-profit venture.
In developing countries like India, however, several public utility services have been accomplished with participation from both the public and private sector, like the metro in Delhi. In many other countries, however, public utility is strictly a job for the government, and private firms are barred from entering.
The main reason for this is because the government can afford to provide quality public utility services at cheaper rates, something that is beyond what private firms can hope to do. This may not be the case in all countries, however, where the quality of service (from the public sector) is as cheap as the fares they are priced at.