Cayman Water
Apply for ServiceRatesWater Quality FactsWater Quality InformationLaws and Regulationsdownloads

Water Quality Facts

Cayman Water piped water is desalinated seawater produced using reverse osmosis desalination. Raw feed water is extracted from wells drilled deep into the limestone bedrock beneath the Island. This water is pristine seawater with none of the contaminants usually associated with open seawater sources.

Salt in the seawater is separated from the fresh water using a process called reverse osmosis. This process pressurizes the seawater and semi-permeable membrane elements allow freshwater to pass through to one side of the elements leaving brine water and contaminants on the other. The fresh water is then finished in the post treatment process to produce potable water that is healthy and wholesome to drink.

  1. Water Quality
    • Total Dissolved Solids ≤ 200 ppm (parts per million)
    • pH = 7.00 average
    • chlorine = 0.25 ppm free average
    Seawater TDS (total dissolved solids) are approx. 38,000 ppm so 99.5% of the salt is separated from the seawater to make fresh drinking water.
  2. Total Dissolved Solids Breakdown (major constituents)
    • Alkalinity as CaCO3  -  5 to 12 ppm average
    • Total hardness as CaCO3  -  10 to 20 ppm average
    • Sodium as Na  -  95 ppm average
    • Chloride as Cl  -  65 ppm average
  3. Finished water chemical additions

    • Chlorine (calcium hypochlorite) dosed to achieve 0.25 ppm free chlorine residual.
    • pH stabilizer- a high grade sodium hydroxide, dosed to achieve +7.00 pH.
    • Corrosion inhibitor- a zinc-orthophosphate polymer dosed to achieve 0.5 ppm Zn and control corrosion below 5 mpy for mild steel.
  4. Testing

    • Daily - twelve samples, TDS, Conductivity, pH, chlorine, hydrogen sulfide, corrosion.
    • Weekly - five samples, sodium, chloride.
    • Monthly - 63 samples, total coliform, faecal coliform, by Water Authority-Cayman, three samples, mass spectrum analysis for TDS breakdown tested by overseas lab.
    • Annually - 3 sets of samples for inorganic chemicals, organic chemicals (pesticides and volatile organics), disinfection by-products, and microbiological contamination tested by overseas lab.


Memberships & Useful Links: