Seawater Treatment to Drinking Water: Steps and Technology

Short answer: seawater is most commonly turned into drinking water with seawater reverse osmosis (SWRO), but the membrane is not the first step. A workable system starts with intake screening, coarse solids removal, pretreatment to control turbidity and biofouling, cartridge filtration, chemical dosing, SWRO membranes, and then post-treatment such as remineralization, pH correction, and disinfection. For projects in Indonesia, product water still needs to be verified against applicable drinking-water requirements, and reject brine needs to be addressed in the environmental permitting review.

Image of a modern seawater treatment plant

Why is Seawater Treatment Important?

Desalination matters for coastal areas, small islands, resorts, industrial facilities, vessels, and utilities that do not have a stable freshwater source. Seawater is abundant, but its salinity means it cannot be used directly as drinking water or as sensitive process water.

Reverse osmosis (RO) is the preferred technology for many projects because it works as a pressure-driven membrane process. DuPont’s technical manual describes RO as a process used for seawater and brackish-water desalination, and notes that RO pressure can range from about 5 bar for brackish water to more than 84 bar for seawater, depending on design and feed salinity. Toray also classifies seawater RO membranes for seawater or high-salinity sources above 10,000 ppm.

Steps in the Seawater Desalination Process

The basic SWRO sequence should be viewed as membrane protection, not just as an RO skid. The intake collects seawater from a beach well, shoreline intake, or offshore intake. Screens and initial solids removal protect the system from trash, sand, shells, and large suspended particles.

Pretreatment then reduces fouling risk. Common options include multimedia filtration, ultrafiltration, cartridge filtration, antiscalant dosing, dechlorination where oxidants are present, and pH control based on water analysis. After the SWRO membrane separates permeate from concentrate, product water usually needs post-treatment so it is stable, less corrosive, and suitable for its final use.

SWRO Pretreatment Checklist

Design decision	Number or parameter to check	Why it matters	Component handoff
Salinity and source type	TDS, conductivity, temperature, pH, tidal variation	Decides whether BWRO is enough or SWRO is required, and sets early pressure and recovery assumptions	Industrial RO membranes
Particulate fouling	Turbidity, TSS, SDI15	DuPont requires FilmTec RO/NF feedwater SDI15 to be less than 5.0	Cartridge filters and pretreatment media
Biofouling	Bacteria, algae, TOC, intake condition	Warm, organic-rich seawater can plug membranes quickly	Media pretreatment, UF, and controlled upstream disinfection
Oxidants and chlorine	Free chlorine, ozone, ORP	Toray stresses that there should be no trace of chlorine in RO membrane feed; residual chlorine requires dechlorination	Dosing pumps for sodium bisulfite or related chemicals
Scaling	Calcium, magnesium, sulfate, barium, strontium, silica, alkalinity	Determines antiscalant dosage, safe recovery, and cleaning schedule	Antiscalant dosing and scaling analysis
Membrane housing	4 inch or 8 inch diameter, elements per vessel, pressure rating	Determines footprint, capacity, and mechanical safety of the RO skid	Codeline pressure vessels
Product water	TDS, pH, alkalinity, boron where relevant, microbiology	Determines whether second-pass RO, remineralization, UV/ozone, or storage controls are needed	Post-treatment, UV/ozone, and instrumentation
Reject brine	Concentrate flow, salinity, residual chemicals, discharge point	Needs review against technical approval, operating permits, and receiving-water limits	Environmental review and RO chemical program

Key Technologies in Seawater Treatment

The main technologies used in seawater treatment are reverse osmosis (RO) and distillation. In RO, a high-pressure pump pushes seawater across a semi-permeable membrane. Product water is called permeate, while the concentrated salt stream leaves as concentrate or reject.

Membrane selection should follow feedwater quality and the product-water target. Watermart supplies SWRO component options such as DuPont FilmTec seawater membranes and Toray RO membranes. Watermart’s Toray seawater product data lists examples such as TM820V-400 with 9,000 GPD permeate flow and 99.8% stabilized salt rejection, and TSW-400LE with 6,100 GPD permeate flow and 99.6% stabilized salt rejection under manufacturer test conditions. These numbers help with early comparison, but final design still needs salinity, temperature, recovery, fouling risk, and vessel configuration.

Thermal distillation remains useful in some conditions, especially where waste heat or thermal utilities are available. For many modern commercial and industrial projects, SWRO is more practical because the components are modular, expandable, and measurable through pressure, flow, conductivity, and TDS instrumentation.

Challenges and Solutions in Seawater Desalination

The main SWRO challenges are energy use, fouling, scaling, corrosion, product-water stability, and reject-brine disposal. These are not solved by simply buying the most expensive membrane. They are controlled by collecting feedwater data, respecting operating limits, and planning maintenance from the start.

For polyamide RO membranes, oxidants are a major risk. DuPont’s limiting-conditions document states that feedwater must not contain oxidizing agents such as chlorine or ozone, and that SDI15 must be less than 5.0. Toray’s handling manual also requires no trace of chlorine in RO membrane feed; if residual chlorine is present, it needs to be removed with sodium bisulfite and enough contact time. Any system that uses chlorination at intake therefore needs controlled dechlorination before the membrane.

From a regulatory perspective, product water intended for drinking should be tested against the drinking-water parameters that apply in Indonesia at the time of commissioning. The health-environment regulation status changed in 2026: the Ministry of Health JDIH lists Permenkes No. 2 of 2023 as no longer in force, while Permenkes No. 3 of 2026 revokes Permenkes No. 2 of 2023 except for several articles and their appendices. For real projects, confirm the active parameter list with the regulator or accredited laboratory during permitting. For concentrate discharge, early references include Government Regulation No. 22 of 2021 on environmental protection and management and Ministry of Environment and Forestry Regulation No. 5 of 2021 on technical approval and operational feasibility letters for pollution-control activities.

If the project needs antiscalant, sodium bisulfite, membrane cleaners, or an RO chemical dosing program, that step should be discussed with a chemical treatment team. See RO antiscalant and membrane cleaning chemicals from Beta Pramesti for the chemical side of the project.

Initial Sizing Data to Prepare

Input data	Common unit	Impact on SWRO design
Product-water demand	m3/day or m3/hour	Sets membrane count, pumps, vessels, and product tank size
Seawater TDS/conductivity	mg/L or uS/cm	Determines SWRO selection, pressure, salt passage, and possible second pass
Water temperature	degrees C	Affects flux, pressure, and salt passage; DuPont lists a general feedwater limit below 45 degrees C unless the product datasheet states otherwise
SDI15 and turbidity	SDI15, NTU	Determines whether multimedia filtration, UF, or staged cartridge filtration is needed before RO
Recovery target	% permeate from feed	Excessive recovery increases scaling risk and can reduce permeate quality
Operating pressure	bar or psi	Determines high-pressure pump, piping, valve, and pressure-vessel specifications
Product-water target	TDS, pH, hardness, microbiology	Determines remineralization, pH correction, UV/ozone, or additional polishing
Reject brine	m3/hour, TDS, residual chemicals	Determines diffuser design, equalization, monitoring, and environmental documents

The Future of Desalination: Innovations and Trends

The future of desalination is not only about new membrane materials. Many plants gain more value from stable pretreatment, energy recovery, online instrumentation, and disciplined maintenance routines. Monitoring differential pressure, permeate flow, permeate conductivity, pH, ORP, and chemical consumption helps operators see fouling before production drops severely.

For buyers, the safest sequence is to start with feedwater analysis and the final water-use target, then select the intake, pretreatment, membrane, pressure vessel, dosing, and post-treatment configuration. PT Watermart Perkasa can help prepare components such as DuPont FilmTec SWRO membranes, Toray RO membranes, cartridge filters, dosing pumps, and Codeline pressure vessels for desalination projects, retrofit work, or component replacement.

Daily SWRO Operation Checklist

Record feed pressure, concentrate pressure, permeate pressure, and differential pressure for each stage.
Record feed, permeate, and concentrate flow, then calculate actual recovery.
Measure permeate conductivity/TDS and compare it with the commissioning baseline.
Confirm that residual chlorine or other oxidants are not entering the RO membrane.
Monitor SDI15 or at least turbidity after pretreatment, especially during rainy season, high tide, or algae events.
Check antiscalant and sodium bisulfite dosing: tank level, pump stroke, control signal, and injection point.
Replace cartridges based on differential pressure, not only by calendar interval.
Keep cleaning records: date, chemical, pH, temperature, duration, and performance change after CIP.
Test product water regularly according to final use and regulator requirements.