> Many data centres use water-based systems to cool the plant with towers evaporating the heat, like a huge perspiration system, which means that the water is lost.
Someone doesn't know what "evaporation" or "lost" means.
Total datacenter energy use is on the order of 1PWh/yr. Total global solar surface irradiance is on the order of 400,000PWh/yr.
The direct heat contribution is negligible to global temperature.
There is an argument that water vapour in the atmosphere is a greenhouse gas, but also an argument that clouds reflect solar energy, and that this water vapour is emitted at ground level. I don't think it's so obvious that water evaporation from datacenter cooling systems is directly either good or bad for global heating.
There certainly are negative environmental and social effects of this water usage in some places and implementations, and certainly it could include severe heating potential, but this is an over-reduction without further context.