How to Choose the Right Flow Rate for Commercial Water Purifiers

As water purifiers gradually replace bottled water, more and more schools, factories, offices, communities, and hospitals are adopting centralized drinking water systems.

Compared with bottled water, water purifiers are more economical, hygienic, safer, and easier to manage.

However, many distributors face a common question when handling projects:

👉 How do we select the correct capacity (flow rate) for a commercial water purifier?

Choosing a model that is too small results in insufficient water supply, while selecting an oversized system increases unnecessary investment cost.

This guide explains a simple and practical calculation method.

1. Why Reverse Osmosis (RO) Systems Are Widely Used in Projects

For direct drinking water projects, reverse osmosis systems are commonly selected because they offer:

• High filtration accuracy
• Stable water quality
• Compliance with drinking water standards
• Suitability for centralized supply systems

Therefore, commercial system selection is usually based on the RO production capacity (GPD).

2. Gallon-to-Liter Conversion

Commercial RO systems are rated in GPD (gallons per day).

1 gallon ≈ 3.785 liters

Examples:

• 100 GPD ≈ 378.5 L/day
• 500 GPD ≈ 1892.5 L/day
• 1000 GPD ≈ 3785 L/day

3. Determine Daily Water Consumption per Person

In engineering projects, a commonly used reference value is:

👉 2 liters per person per day (within about 8 working hours)

This includes:

• Direct drinking
• Tea / coffee preparation
• Basic daily water usage

4. Example Calculation: School with 500 People

Assumptions:

• Number of users: 500
• Water consumption per person: 2 L/day

Step 1 – Total Daily Water Demand

500 × 2 = 1000 liters/day

Step 2 – Convert to GPD

1000 ÷ 3.785 ≈ 264 GPD

Step 3 – Convert to Required System Capacity

RO systems are rated on 24-hour production, while most water usage occurs within 8 hours.

Formula:

(24 ÷ 8) × 264 × 1.3

= 3 × 264 × 1.3
≈ 1029 GPD

Recommended Selection

Choose a 1000 GPD RO system for this project.

5. Universal Formula

Required GPD = (Number of users × 2 ÷ 3.785) × (24 ÷ 8) × 1.3

Where:

• 2 = liters per person per day
• 3.785 = liter-to-gallon conversion
• 8 = peak usage hours
• 24 = RO system rated production time
• 1.3 = safety factor

6. Why Add a Safety Factor?

A 30% safety margin accounts for:

• Peak usage periods
• Seasonal consumption increases
• Flow reduction due to filter aging
• Possible future increase in users

This helps prevent water shortages and costly system upgrades later.

7. Benefits of Proper Flow Rate Selection

Correct sizing ensures:

• Stable water supply
• Lower operational risk
• Higher customer satisfaction
• Optimized investment cost

Conclusion

Commercial water purifier selection does not need to be complicated.
With a simple calculation method, distributors can quickly determine the correct system capacity.

For project distributors, knowing how to calculate flow rate is more important than simply selling equipment.