Why is the steam from cooling towers not used? If I see the steam coming out of cooling towers at an altitude of 200 meters, I cannot help but think that this energy is wasted. My question is: Why isn't this steam cooled enough to become water and used to create hydroelectric power due to the drop from 200 meters?
 A: There are a number of issues with recovering the energy (mechanical or thermal) from the stack exhaust of a cooling tower.
First, the temperature and energy (enthalpy) of the exhaust is too low to effectively recover. The exhaust is full saturated or over saturated air typically at a temperature of 110 F, not above 120 F.
Second, the amount of water discussed above is way too high. The evaporation rate for a cooling tower can be estimated at 0.8% of the circulating water rate per 10 F of range. For a typical power plant this will max out at 2.0% of the cooling towers flow rate.
A typical 2X1 combined cycle plant has a 125 to 150 MW steam turbine. This equates to about 1,300 gallons per minute of evaporation (177 lbs/sec). Assuming that you could collect all of the water and channel the flow to be able to generate hydroelectric power from a turbine is 10% of the value discussed above, or 20 kw (assuming a 100% efficient cycle, which goes against entropy and the 2nd law).
Cooling towers have been around and in use for a long time and in a lot of applications beyond power generation (petro-chem, refineries, building HVAC, etc.) and there has yet to be a cost effective way to harness the waste heat. Some btu's are just not worth trying to collect and are better sent to the universe to increase universal entropy.
A: Let us see -- how much water per second is getting at the height?
Let's estimate it as 1 ton of water per second. 
Then the energy you can extract form the water is:
$$ 1 [\mbox{ton/s}] * 200 [meters] * g \simeq 20000000 J/s = 2 \mbox{megaWatts}$$
Compared to hundreds or even thousands of megawatts produced and the power plants -- doesn't worth the fuss. And I'm pretty sure that it is a huge overestimation anyway. 
