All three hold water. That is where the similarity ends. A tank that is perfectly good for fire reserve will fail a potable water audit in three places: lining certification, cross-connection and disinfection access.
Potable water tanks
Lining must be certified food-contact grade: pure epoxy or solvent-free polyurethane, with NSF/GB approval as applicable
Interior welds coated continuously; holiday spark test at specified voltage
First-flush and draining arrangement; no dead legs
Access manhole lockable, screened vent, insect-proof
Disinfection: superchlorination on commissioning, rinse to <0.5 mg/L residual
Inspection: annual internal check, coating condition log, bacteriological sample
Fire water tanks
Lining can be epoxy coal tar or pure epoxy; food grade not required
Capacity set by hydraulic calculation (sprinkler + hose + duration), not a round number
Suction nozzle positioned above sediment but below low-level alarm
Freeze protection where climate demands it: insulation, heat trace, or locate below frost line
Inspection: monthly level and pump-start test, annual full-capacity drain test
Process water tanks
Lining matched to chemistry: pH, chloride, temperature, cleaning chemical
Often paired with a treatment system: softener, RO permeate, cooling tower makeup
Level instrument must suit turbulent or aerated service-stilling tube or guided-wave radar
Cross-connection: process and potable headers must be air-gapped, never direct-tied
FAQ snippet
"Can one tank be both potable and fire reserve?" Only with a dedicated partition and separate outlets, or by using a treated-effluent line to refill the fire tank-never by sharing the same compartment, because backflow can contaminate the drinking supply.
Specifying the three service types separately is what turns a generic "water tank" line item into a compliant system.
