Real-time data is not cheap be it financially or overhead on resources.
To enable this using a Web Api would require long polling which is not the best way of doing it and have can be very costly on resources (Database hits every half-a-second!). This would give the appearance that data is real-time.
Alternatively one can look at SQL Service broker using sqldependency as signalr. The initial setup can be tricky. Signalr does have a list of limitations though.
I would suggest looking at technologies like RethinkDB or Firebase for real-time data feeds. There are financial cost implications though. One can also look at the combination of socket.io and react.js/node.js.
Companies like LinkedIn and AirBnb make use of Kafka which is distributed messaging system for real-time notifications. Facebook makes use of a combination of technologies.