Harvesting Systems for Cooling Towers


Many commercial buildings are cooled with systems using evaporative towers and cooling water systems that can be tremendous consumers of potable water. For example, a 200,000 square foot building with 1,000 tons of cooling can consume 2-3 million gallons of potable water in one season! In warmer climates, the consumption can even be greater. Obviously, these heavy consumers need to be evaluated and addressed in a holistic approach to water sustainability in commercial buildings.


Wahaso designs and builds systems that harvest rainwater for cooling tower make-up – saving millions of gallons of water per year. Because of their high consumption of water during a cooling season, evaporative cooling towers and cooling water systems are an excellent use for water harvested from rainwater or other on-site sources of non-potable water. In colder climates that experience frozen precipitation during the winter months, the demand by cooling towers coincides with the warmer months when rainwater is available for harvesting.


Rainwater is an excellent source for cooling tower make-up – even better than municipal drinking water! As water is recirculated over cooling fins in the system, it evaporates and leaves behind whatever dissolved solids were in the water source. Rainwater is naturally “soft” with almost no dissolved solids. That means that the water in the tower can be cycled more times before it must be flushed out in the “blow down” process. Blow down can account for 25% of total cooling tower water usage, resulting in the discharge of hundreds of gallons at time, so increasing cycles saves lots of water. Also, most towers have water treatment for water hardness and algae, so increasing cycles saves a significant amount of chemicals over time. Using rainwater for towers saves drinking water that would otherwise be evaporated, saves water that would be wasted in the blow-down process, and saves chemical costs and chemical pollution – a very green thing to do!

The high demand by cooling towers can easily outpace rooftop rainfall – even from buildings with large roof areas. In these cases, we recommend adding additional sources of harvested water – parking lot stormwater and treated greywater are also good water sources. Underground cisterns can effectively store millions of gallons of stormwater while greatly reducing water run-off from the property. Water from the harvesting system storage tank is directed to the cooling tower “make-up” inlet. Water chemistry is critical to cooling tower efficiency and may require additional filtration or additives before adding to make-up.


During the cooling season when towers are running everyday, most systems will quickly evaporate harvested rainwater. But it is during these peak periods when the amount of condensate from the blowers will peak. Condensate is an excellent source for reuse in towers either as a supplement to rainwater or other on-site sources, or as a source on its own and a typical commercial building will generate thousands of gallons per day. Condensate harvesting systems are relatively inexpensive, with an attractive return on investment. To see a case study on one our systems that used cooling condensate for cooling tower make-up, click here. Wahaso is happy to talk with you about your cooling system and the opportunities for saving water or applying harvested water- contact us today!

Condensate Harvesting Wahaso’s standard system for harvesting condensate. System can save 10,000-gallons per day.