Some chillers will function as heat exchangers between the condensing water and chilled water when off in a 'free-cooling' mode. The refrigerant is allowed to move via natural circulation, and transfers heat from the chilled water to the condensing water. usually takes at least 5 deg difference between the chilled water return and the condensing water supply for it to establish a decent enough flow, so if you are looking for a semi-usable chilled water temp, the wet bulb would usually have to be down in the low 40's (this is not difficult in dry climates).
If the 5° difference is hard to attain, many sites also have a large heat exchanger between chilled water and condensing water that can use coolnig tower only cooling with slightly higher water temps.