Well yield is an important factor when designing a borehole water RO system. If the well cannot provide enough raw water, the RO system may experience low inlet pressure, frequent shutdowns and unstable production.

The RO capacity, recovery rate and storage tanks must therefore be designed according to both the daily water demand and the well’s sustainable yield.

 

What Is Well Yield?

Well yield is the amount of water a borehole can supply continuously, usually measured in m³/h.

Design should be based on the sustainable well yield, not only the maximum pumping rate. Seasonal groundwater changes, drawdown and recovery time must also be considered.

A pumping test should confirm:

• • Sustainable flow rate
• • Static and pumping water levels
• • Water-level recovery time
• • Seasonal minimum yield
• • Changes in raw-water quality

 

How Well Yield Determines RO Capacity

An RO system requires more feed water than its rated product-water capacity because part of the feed becomes concentrate.

Use the following calculation:

RO Feed Flow = Product-Water Flow ÷ Recovery Rate

For example, a 4 m³/h RO system operating at 65% recovery requires:

4 ÷ 0.65 = 6.15 m³/h of feed water

If the well can continuously supply more than 6.15 m³/h, it may feed the system directly through a raw-water tank. If the yield is lower, additional storage or longer well-pumping hours may be required.

View our customized borehole water treatment systems for groundwater purification projects.

 

Can a Storage Tank Solve Low Well Yield?

A raw-water tank can balance the difference between the well yield and the RO feed flow. However, storage cannot solve an insufficient total daily water supply.

For example:

• • RO product capacity: 4 m³/h
• • RO operating time: 10 hours
• • Recovery rate: 65%
• • Daily RO feed requirement: 61.5 m³
• • Sustainable well yield: 4 m³/h

During RO operation, the hourly raw-water shortage is:

6.15 − 4 = 2.15 m³/h

 

For ten hours, the calculated shortage is:

2.15 × 10 = 21.5 m³

The usable raw-water tank volume should therefore exceed 21.5 m³ and include an appropriate operating reserve.

However, if the well cannot produce at least 61.5 m³ per day, increasing tank size will not solve the long-term shortage. The project may require longer pumping hours, a smaller RO system, another well or an alternative water source.

 

Raw-Water Tank and Product-Water Tank

The two tanks perform different functions.

 

Raw-Water Tank

The raw-water tank:

• • Balances unstable well flow
• • Prevents feed-pump dry running
• • Provides stable water to the RO pretreatment system
• • Allows oxidation, aeration or sediment settling when required

 

Product-Water Tank

The product-water tank stores treated water and balances factory demand when the RO system is stopped or producing less than the peak consumption rate.

Its volume depends on:

• • Maximum hourly water demand
• • Daily operating hours
• • Production peak periods
• • Cleaning and maintenance downtime
• • Required emergency reserve

Product-water storage should be calculated from the actual consumption schedule rather than selected only as a percentage of daily production.

 

Recommended Design Process

A practical design sequence is:

1. Confirm the required daily product-water volume.
2. Determine how many hours the RO system will operate.
3. Calculate the required hourly RO capacity.
4. Select a realistic recovery rate from the water analysis.
5. Calculate the total feed-water requirement.
6. Compare it with the sustainable well yield.
7. Size the raw-water and product-water tanks.
8. Add suitable pretreatment according to the water quality.

Where turbidity, colloids or microorganisms are unstable, review whether the borehole water needs ultrafiltration before RO.

 

Common Design Mistakes

Avoid the following mistakes:

• • Selecting RO capacity only from daily demand
• • Using maximum well-pump flow as sustainable yield
• • Ignoring the RO recovery rate
• • Oversizing the RO system without enough raw water
• • Using storage tanks without checking the daily water balance
• • Ignoring seasonal changes in well yield
• • Installing insufficient pretreatment

An undersupplied RO system may show symptoms similar to equipment failure. Read more about low RO permeate flow and its causes.

 

Information Required for System Design

Before choosing an industrial reverse osmosis system, provide:

• • Sustainable well yield
• • Pumping-test results
• • Complete water-quality report
• • Required product-water capacity
• • Daily operating hours
• • Product-water standard
• • Intended water use
• • Peak hourly water demand
• • Available space for storage tanks

 

Conclusion

Well yield directly affects RO capacity, operating hours and storage-tank volume. A large RO system will not produce stable water if the borehole cannot supply sufficient feed water.

The correct design should balance sustainable well yield, RO recovery, daily water demand and storage requirements. Send Zhongnuo Water Treatment your pumping-test results, water analysis, operating hours and water application to receive a suitable borehole water treatment proposal.

 

FAQ

Can the RO capacity be higher than the well yield?

Yes, but only when a raw-water tank stores enough water before operation and the well’s total daily supply meets the RO feed requirement.

 

Does a larger raw-water tank increase well yield?

No. It only stores water and balances flow differences. It cannot increase the amount of water available from the borehole.

 

Should RO capacity equal daily water demand?

No. Hourly RO capacity is calculated from daily demand and the planned operating hours.

 

Why does RO feed flow exceed product-water flow?

Because part of the feed water leaves the RO system as concentrate. The actual feed requirement depends on the designed recovery rate.