A reality check on water balance

By Dani Sheehan.

Water balance is about chemistry, not just hitting the numbers.

Water balance applications have become popular tools for calculating the Langelier Saturation Index (LSI) of a swimming pool or hot tub to determine whether the water is balanced, corrosive or scale-forming. While these tools offer convenience, relying on them without a solid understanding of water chemistry can lead to inconsistent results and even dangerous chemical adjustments.

The Pool and Hot Tub Alliance (PHTA) offers a Water Balance Fact Check to outline the requirements according to ANSI/APSP/ICC-11 2019 “American National Standard for Water Quality in Public Pools and Spas.”  

The limits of LSI apps

Several chemical manufacturers and independent developers have created water balance apps that offer dosage recommendations based on LSI values. However, recent testing has revealed a wide range of inconsistencies among these apps, particularly in:

• The use of outdated LSI ranges (e.g., +0.3 instead of the current +0.5 upper limit)
• Simplified or incorrect Total Dissolved Solids (TDS) correction factors
• Allowing inputs outside of acceptable ranges just to achieve a balanced LSI result

This can result in chemical treatments that appear to correct LSI – but violate industry standards or create new imbalances in the water chemistry.

LSI is a guide

LSI is a helpful indicator, but balanced water chemistry depends on maintaining proper values across all parameters. In fact, it’s possible to see an out-of-range LSI even when all other parameters are within their ideal limits due to other influences like saltwater chlorine generators or specialty chemicals.

In short: a balanced LSI does not always mean safe or stable water.

What can you do?

1 – Stay current: Always follow the most recent ANSI/APSP/ICC-11 standards and use the 2024 edition of the “Pool & Spa Operator Handbook” for guidance on proper calculations.

2 – Use apps with caution: Apps are tools – not substitutes for professional judgement. Double-check any recommended chemical dosages and avoid apps that allow inputs outside accepted parameter ranges.

3 – Understand local regulations: While most health departments require records for pH and sanitizer levels, they may not require documentation for alkalinity, hardness, TDS or LSI. Still, it’s your responsibility to ensure balanced water using all the relevant data.

4 – Consult trusted resources: For further education, training and certification, connect with the PHTA for the industry’s standardized information and your own professional development.

Read the full Water Balance Fact Check for additional considerations and to see the recommended water balance values.