March 19, 2008 Salt Water Definition Review According to the Water Quality Association the following definitions would apply to drinking water. • Fresh Water- <1,000 TDS • Brackish Water- 1,000- 5,000 TDS • Highly Brackish Water- 5,000- 15,000 TDS • Saline Water- 15,000- 30,000 TDS • Sea Water- 30,000- 40,000 TDS • Brine- 40,000- 300,000+ TDS In discussions with engineering firms designing life support systems for aquariums and zoos the following guide lines were provided: • Fresh Water- <1,000 TDS • Brackish Water- 1,000- 20,000 TDS • Salt Water- 20,000- 36,000 TDS Notes: • Fresh water fish can survive in water with a TDS of 2,000. • They will try to utilize plastic or titanium material where possible. • They experience corrosion with cast iron pumps at a TDS under 1,000 which is more pronounced with intermittent use. Impact on Materials • PVC pipe and most rubber gasket & seal materials are rated for sea water applications up to 140º F. • Fiberglass is less prone to blistering in sea water applications due to a similar concentrate of solute resulting in less pressure gradient in the FRP laminate. • Most heater manufacturers are limiting warranty of standard heaters to a maximum TDS of 2,000. When heaters are installed in applications with a TDS higher than 2,000, the manufacturers are recommending alternate heat exchanger material (Cooper Nickel) and heat exchanger flow velocities of 12 ft/ sec instead of the standard 6 ft/ sec. • Pump manufacturers are experiencing some corrosion problems with bronze fitted impellers and are reducing the Zinc content to the point the impeller is virtually all copper. In elevated TDS levels or intermittent use, they are recommending epoxy coating of cast iron pumps due to corrosion and pitting. This can be very pronounced if air is introduced into the pump.
