Shades of Gray

Today there are water issues throughout the world, which also affects data centers.  Ten states in the U.S. are in longstanding battles over water rights while river and lake water quality has been diminishing across southern Europe, India, and the Middle East.  In the U.S. drought conditions have affected 50 to 60% of states yet about 30% of the 26+ billion gallons used daily is sent outside for landscaping and 10-15% is used by building occupants.  With temperature records increasing every year, water shortages are likely to be part of our future planning, even with aggressive water management and conservation.  And water utility rates are increasing by 8-10% per year. 

To relieve this concern of scarcity we need to consider water recycling.  This means reusing the most viable type of wastewater: graywater.  Graywater is wastewater from sinks, showers, dishwashers, drinking fountains, and cooling towers; it does not include any water that might have ever come in contact with fecal matter (black water).  Graywater can have a few varieties and many systems might have an issue with water that has grease, food remnants, and other contaminants that make the water harder to use. 

On-site wastewater treatment and reuse are considered tertiary systems to the primary goals for most locations.  However, in locations with water shortages now and likely to continue into the future, graywater reuse has been implemented.  Regulations have varied from state to state and country to country, but more have seen the value and adopted their own with local adaptations, especially in the arid locations.  Using graywater with a treatment system jointly with other methods of water reduction can yield a large reduction of a data center’s potable water consumption. 

Graywater system setup usually has a basic setup of components: collection at the sources; piping to transport to storage tanks; filtering and treatment system; pumping to deliver; and devices to monitor and control the overall process.  For most graywater systems, getting and using the water within 12 to 24 hours is part of the use plan to prevent it from settling too much, breaking down, and causing issues in the piping or storage tanks.  With a data center using cooling towers for heat rejection this isn’t an issue as graywater is used continuously to supplement the cooling tower water needs.  In most cases the amount of water gained on site is miniscule to the overall water use plan for the data center.  Using 10,000 gallons a day per megawatt is not uncommon and the other uses may only add up to 1,000 per day on a peak day. 

Stormwater can also be handled on site with a cistern used for collection for reuse, but it should be noted that some locations do not allow stormwater collection as this can be associated with the water rights for the region.  Also, there is a shortage of time to obtain regulatory approval as such systems can lengthen the time of a permit review, especially in states with water shortage issues.  And even with proper planning the return on investment period may seem too long as well as a hassle for maintenance.  That ROI is very dependent on location, water cost, quality, and the type of treatment system. 

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