How to Read a Boiler Water Analysis Report

A boiler water analysis report can look like a wall of numbers if you're not the one who reads them every day. In practice, five or six parameters do most of the work of telling you whether your program is on target. Here's what to look at first, and what an out-of-range number usually means.

Feed water vs. boiler water vs. condensate

Most reports test three separate samples, and it's worth knowing why: feed water shows what's going into the boiler, boiler water shows what's concentrating inside it, and condensate shows whether anything is coming back corroded or contaminated. A problem that only shows up in one of the three tells you where to look.

The parameters that matter most

Total Hardness (as CaCO₃)

Hardness in feed water is the single biggest predictor of scale risk. Softened feed water should read close to zero; anything meaningfully above that means your softener needs attention before it means your chemical dosing does.

Alkalinity (P and M alkalinity)

Alkalinity affects both scale formation and the risk of caustic embrittlement at higher pressures. It's read alongside pH — a boiler running high alkalinity and high pH needs a different chemical strategy than one running near-neutral.

TDS / Conductivity

This is your blowdown control number. As TDS climbs toward the ceiling set for your operating pressure, blowdown rate needs to increase — otherwise you risk carryover and scale-forming salts depositing on tube surfaces.

Silica

Silica scale is harder to remove than calcium scale and insulates heat transfer surfaces badly even in thin layers. High-pressure boilers in particular need silica tracked closely against their TDS limit.

Sulphite Residual (or other oxygen scavenger residual)

This confirms your oxygen scavenger is dosed correctly. Too low, and dissolved oxygen is free to pit the boiler and condensate lines; too high wastes chemical and can affect steam purity.

pH

Boiler water pH is normally kept in an alkaline range to minimise corrosion, but the right target depends on your metallurgy and pressure — this is usually set specifically for your system rather than taken from a generic chart.

What to do when a number is out of range

• Hardness creeping up: Check the softener regeneration cycle before adjusting chemical dosage.
• TDS trending high: Increase blowdown rate, and confirm the blowdown control system is actually responding to your conductivity setpoint.
• Sulphite residual low or erratic: Check dosing pump calibration and injection point — a common cause is a pump losing prime, not an underdosed program.
• Silica rising toward the limit: Reduce cycles of concentration via increased blowdown, since silica doesn't respond to chemical treatment the way calcium scale does.

The bottom line

A water analysis report is only useful if someone is actually acting on the trend, not just the single reading. That's why an ongoing program includes regular testing and a written interpretation — not just a one-time lab result.