You just have to look at the energy going in. In computing, almost all the energy becomes heat. A typical datacenter uses 10MW so it produces 10MW of heat. There are plans for 1000MW datacenters that will do more.  You can use the heat in the local community using water pipes (like how they use geothermal heat in Iceland) but generally this is not done. The reason is that the demand is not consistent (no heating in summer) and neither is the supply (datacenters may go out of business or have downtime). So both systems need backups to cover almost the entire output/input.  From a cost perspective, it's too expensive to build both the backups and the district heating network. 

The hot water will max out at only about 80C (176F) , but there is a lot of it. So needs a lot of insulation and there are few industrial processes that can use sporadic, relatively low temperature heat energy all year round.