About 5 S/m. 5 S/m (i.e., sea water's conductivity is one million times higher than that of deionized water).
Measurements of the effect of pressure on the electrical conductivity of seawater were made for salinities of 2, 14, 22, and35permilover pressure and temperature ranges of 0 to 1000 bars above atmospheric pressure and the freezing point to30degC, respectively.  The conductivity of seawater is dependent on the salinity and temperature of the water 38. Measurements will vary between the Equator and the poles as well as with depth due to conductivity’s dependence on temperature 38. As with conductivity, the expected salinity of a body of water can only be estimated. When water temperature increases, so will conductivity 3. For every 1°C increase, conductivity values can increase 2-4% 3. Temperature affects conductivity by increasing ionic mobility as well as the solubility of many salts and minerals 30. Definition and description. Conductivity of a substance is defined as ' the ability or power to conduct or transmit heat, electricity, or sound '. Its units are Siemens per meter [S/m] in SI and millimhos per centimeter [mmho/cm] in U.S. customary units. Its symbol is k or s. Ordinary distilled water in equilibrium with carbon dioxide of the air has a conductivity of about 10 x 10 -6 W -1 *m -1 (20 dS/m). Because the electrical current is transported by the ions in solution, the conductivity increases as the concentration of ions increases. High quality deionized water has a conductivity of about 5.5 μS/m, typical drinking water in the range of 5-50 mS/m, while sea water about 5 S/m (i.e., sea water's conductivity is one million times higher than that of deionized water). Conductivity (or specific conductance) of an electrolyte solution is a measure of its ability to conduct electricity. The SI unit of conductivity is siemens per meter (S/m). While freshwater sources have a low conductivity and seawater has a high conductivity, there is no set standard for the conductivity of water. Instead, some organizations and regions have set limits on total dissolved solids for bodies of water 14,37. When water temperature increases, so will conductivity 3. For every 1°C increase, conductivity values can increase 2-4% 3. Temperature affects conductivity by increasing ionic mobility as well as the solubility of many salts and minerals 30. Temperature changes will have a greater effect on the conductivity of deionized water (or any nearly pure water), due to the molar equivalent conductivity of H+ and OH-in the absence of other ions 3. Instead of increasing conductivity by 2-3% per degree Celsius, it may increase by approximately 5% per degree Celsius 3. When water temperature increases, so will conductivity 3. For every 1°C increase, conductivity values can increase 2-4% 3. Temperature affects conductivity by increasing ionic mobility as well as the solubility of many salts and minerals 30. Water has great abundance on the Earth, and of that abundance about 97% is sea water. Sea water contains about 3.5% by weight of salt (sodium chloride). The salinity does vary, and the combination of salinity and temperature has a major influence on ocean currents and behavior. The salinity of the water is measured with a CTD instrument (Conductivity, Temperature, Depth). The conductivity is used to calculate the salinity in conjunction with the temperature and depth (pressure) measurements. Seawater has an average density of 1.027 gm/cm 3, but this varies with temperature and salinity over a range of about 1.020 to 1.029 Seawater, or salt water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% (35 g/L, or 599 mM), which is a specific gravity of about 1.025. This means that every kilogram (roughly one litre by volume) of seawater has approximately 35 grams (1.2 oz) of dissolved salts (predominantly sodium (Na+) and chloride (Cl−) ions). Average density at the surface is 1.025 g / ml. Seawater is denser than both fresh water and pure water (density 1.0 g/ml at 4 °C (39 °F)) because the dissolved salts increase the mass by a larger proportion than the volume. The freezing point of seawater decreases as salt concentration increases. Drinking water 0.005 – 0.05 S/m. Sea water 5 S/m. Electrical Conductivity and TDS. TDS or Total Dissolved Solids is a measure of the total ions in solution. EC is actually a measure of the ionic activity of a solution in term of its capacity to transmit current. Ordinary distilled water in equilibrium with carbon dioxide of the air has a conductivity of about 10 x 10 -6 W -1 *m -1 (20 dS/m). Because the electrical current is transported by the ions in solution, the conductivity increases as the concentration of ions increases.
http://academic.research.microsoft.com/Paper/1626086.aspx http://www.fondriest.com/environmental-measurements/parameters/water-quality/conductivity-salinity-tds/ http://www.lenntech.com/applications/ultrapure/conductivity/water-conductivity.htm https://en.wikipedia.org/wiki/Conductivity_%28electrolytic%29 http://www.fondriest.com/environmental-measurements/parameters/water-quality/conductivity-salinity-tds/ http://www.fondriest.com/environmental-measurements/parameters/water-quality/conductivity-salinity-tds/ http://hyperphysics.phy-astr.gsu.edu/hbase/Chemical/seawater.html https://en.wikipedia.org/wiki/Seawater http://www.lenntech.com/applications/ultrapure/conductivity/water-conductivity.htm
typical conductivity of seawater