Re: Build somewhere else?
Unfortunately they won't be able to heat the water enough for this to be useful - data centre cooling is about taking heat away quickly from the hot chips, not letting the water stay there long enough to reach a high temperature.
By low grade heat, I really do mean low-grade - 20-40Celsius. Normal Pool temperatures are ~28C. Underfloor heating wants to be a maximum of 50degrees (unlike radiators which need to be ~60-70).
This isn't about water-cooling or changing anything in the data halls at all - it's a matter of where the heat exchanger pulling heat out of the data hall dumps to (i.e. not the atmosphere please). The DC cooling could either dump to a load directly, or more likely to a big tank of water as a buffer/store, from which a heat-pump on the other side can draw energy as required for district heating or singular loads (like a swimming pool/leisure centre).
The heating demand for a small municipal pool can be 250-300MWh/yr.
A mid-size DC with 1MW IT Load and a PUE of 1.4 can release 3,700MWh thermal per year.
Whilst this might not be practicable for individual DCs, when you consider that they are often clustered (e.g. the multitude of 2-10MW DCs along Buckingham Avenue in Slough), it is both economically and environmentally criminal to be dumping that much heat to atmosphere instead of pooling it into some form of district heating (there's also at least one public sport centre/swimming pool on that trading estate, within half a mile of the DC cluster!).