Water Source Treatment (Well, River, Seawater)

Treating water at the intake, before it ever reaches fish, is the first and cheapest line of defence in biosecurity and water-quality management. Well water is usually pathogen-free but often carries high dissolved CO₂ (10–50 mg/L), iron, manganese, and low dissolved oxygen; degassing cascades plus aeration and manganese-sand filtration to below 0.3 mg/L iron are standard, with occasional ozone or UV for any surface infiltration risk. River and lake water poses the opposite problem: rich in suspended solids (10–500 mg/L seasonally), algae, wild-fish pathogens, and agricultural runoff; typical trains run coarse screening, coagulation-flocculation, sedimentation or dissolved-air flotation, rapid sand filtration, then 30–60 mJ/cm² UV, with residuals checked continuously. Seawater intake treatment centres on filtration to protect pumps and biofilters, macrofouling control, and, in sensitive hatcheries, UF membranes or 1 µm cartridge filtration plus UV to exclude parasite larvae and bacteria. Groundwater high in hardness may need softening or acid dosing to keep pH and alkalinity in target ranges. Every intake design should answer three questions: what organisms and chemicals the source carries at worst-case conditions (flood, algal bloom), which treatment steps remove them, and how the farm is protected if treatment fails, ideally with a raw-water reservoir sized for 1–2 days and automated diversion valves.