A remote island rarely consumes water at the same rate all day, while a seawater RO package performs best against a defined operating schedule. Product-water storage connects those two patterns. Before comparing equipment capacities, document demand, storage that is genuinely usable, power availability and the periods reserved for cleaning or maintenance.
1. Build an hourly demand profile
Separate drinking, accommodation, kitchen, laundry, process, irrigation and fire-service demands. Record normal and peak occupancy, delivery days for visiting vessels, seasonal tourism and any emergency users. Use measured meter totals where available and retain at least one high-demand week. Daily averages alone hide morning, meal-time and vessel-filling peaks that the distribution tank may need to cover.
State which demands require desalinated water and which can use another source. Identify the required quality and verification point for each potable or process stream. Add distribution losses only as a declared planning allowance, not as an unexplained percentage. The final schedule should show hourly demand, daily total, credible peak, seasonal range and any demand that can be postponed during a power or intake interruption.
2. Separate tank volume from usable reserve
List existing and proposed tanks with nominal volume, minimum operating level, overflow level and volume unavailable because of suction, freeboard or water-quality management. Usable storage is the volume between the agreed upper and lower operating levels. Keep fire reserve, emergency reserve and routine balancing volume visible as separate lines so one purpose is not silently counted twice.
Test the balance hour by hour: opening usable storage plus RO production minus consumption equals closing usable storage. As a simple illustration, demand of 120 m³/day and 20 available production hours corresponds to 6 m³/h of average permeate before losses or reserve. If only 16 hours remain after a maintenance or power window, the arithmetic becomes 7.5 m³/h. These figures explain the method; they are not BOKAWATER model ratings or recommended margins.
3. Define the operating window and interruption cases
Describe grid, generator or renewable-power windows, expected voltage and frequency, intake restrictions, tide or turbidity events, operator coverage and permitted noise hours. Reserve time for flushing, chemical cleaning, cartridge changes and planned inspection. Specify whether the plant can start and stop daily, whether tanks provide stable suction to distribution pumps, and how product water is protected during storage.
Run at least normal-day, peak-day, planned-maintenance and credible outage cases. For each case, show available production hours, required permeate, lowest tank level and any demand-management action. Then ask the supplier to present feed, permeate and concentrate flows, pretreatment assumptions, energy boundary, controls and restart procedure. Seawater salinity, temperature and intake quality still govern the engineering projection; storage arithmetic cannot determine recovery or membrane selection by itself.
Data to collect before comparing proposals
| Parameter / interface | Unit / format | Why it matters |
|---|---|---|
| Demand record | Hourly profile and m³/day | Separate normal, peak and seasonal cases. |
| Water uses | Potable, process, service and fire | Assign quality and priority to every use. |
| Usable storage | Upper level minus lower operating level | Exclude freeboard, dead volume and dedicated reserves. |
| Production window | Available hours per day | Deduct cleaning, maintenance and power restrictions. |
| Illustrative duty | Demand divided by available hours | Add only explicit allowances and verify units. |
| Power availability | Grid, generator, renewable schedule | State voltage, frequency and outage scenario. |
| Intake condition | Salinity, temperature, tide and turbidity | Provide seasonal data and sampling point. |
| Interruption cases | Maintenance, intake upset and outage | Track the minimum tank level in each case. |
| Supplier output | Water balance, energy boundary and controls | Require assumptions rather than a capacity label. |
Technical references
- US Department of Energy — REDi Island desalination station ↗Source checked:
Evidence scope — original English record
Describes an island desalination arrangement in which reverse osmosis, energy recovery and final treatment are followed by storage for later distribution.
- DuPont FilmTec — Reverse Osmosis and Nanofiltration Technical Manual ↗Source checked:
Evidence scope — original English record
Reference for seawater composition, osmotic-pressure implications, typical system recovery context and open-intake biofouling risk; actual design remains source-specific.
- US Department of Energy — Desalination Basics ↗Source checked:
Evidence scope — original English record
Explains membrane desalination, pressure-driven reverse osmosis and production of a concentrated brine stream.
- BOKAWATER — Small desalination plant reference ↗Source checked:
Evidence scope — original English record
Existing BOKAWATER desalination product-family reference only; this planning example does not select or rate a model.