• Drag-out (gal/day or L/day): Solution that leaves the tank on parts/racks/barrels.
• Evaporation (gal/day or L/day): Water that leaves the tank as vapor.
• Replenishment (gal/day or L/day): Water you add back (DI/RO) + chemistry additions you dose.
• Net water change: Whether tank level rises, falls, or stays stable.

Key idea:
Evaporation changes concentration (makes the bath stronger). Drag-out changes inventory (removes both water + chemistry).

At steady operating level (tank level “about the same” each day):

DI Added ≈ Evaporation + Drag-out + Any Bleed/Overflow

If you know any three, you can estimate the fourth.

Water balance equation (daily)

• Let A = added DI water (gal/day)
• Let E = evaporation (gal/day)
• Let D = drag-out (gal/day)
• Let B = bleed/overflow/filter discharge losses (gal/day)
• Let ΔL = level change converted to volume (gal/day)

A = E + D + B + ΔL

If your level is stable, ΔL ≈ 0, so:

A ≈ E + D + B

1) Added water (A)

• Track how much DI goes into the tank (flow meter, makeup log, or tote usage).
• If you don’t have a meter, even “we add ~15 minutes of DI at X gpm” is a usable start.

2) Evaporation (E)

• Best: compare tank level drop during idle (no production) hours.
• Good: estimate from weekly level trend + water added – known losses.

3) Drag-out (D)

Pick one method you can actually do:

Method A — Catch-and-measure (fastest):

• Hold a rack over the tank for a consistent drip time (e.g., 10 seconds).
• Catch the drip in a container and measure volume.
• Multiply by loads/day.

Method B — Weigh a catch pan:

• Weigh an empty pan (or bucket), collect drip, weigh again.
• Convert weight to volume (water-like solutions are close enough for estimating).

Method C — Rinse contamination proxy:

• Use rinse conductivity or titration trend as a “drag-out indicator” (not a direct gallons value, but great for improvement tracking).

4) Bleed/overflow/filter losses (B)

• If you do periodic dumps, convert to a daily average (e.g., 20 gal/week → ~2.9 gal/day).
• Include filter housing dumps, carbon treatments, and maintenance drains if they are routine.

Tank: Nickel process tank
Observed: Level is stable week to week (ΔL ≈ 0)
Measured/Logged:

• Added DI water A = 30 gal/day
• Estimated evaporation E = 12 gal/day
• Filter dump averages B = 3 gal/day

Then:

D ≈ A - E - B = 30 - 12 - 3 = 15 gal/day drag-out

That is a big number—and it usually explains why the bath “consumes” chemistry even when operators feel like they’re doing everything the same.

Once you have drag-out volume, you can estimate chemical inventory loss:

Chemical loss (mass/day) = Drag-out volume (L/day) × Concentration (g/L)

Example:

• Drag-out D = 15 gal/day = 56.8 L/day
• A component concentration is C = 300 g/L

Then:

• Loss = 56.8 × 300 = 17,040 g/day = 17.0 kg/day

This is why drag-out reduction (drip time, rack angle, dwell, drain boards) can be a bigger “savings lever” than negotiating chemical price.

Evaporation removes water only, so concentrations rise, meaning:

• If you “dose to schedule” without checking concentration, you can over-add
• Then later, when workload shifts, you see wild swings and chase the bath

A simple rule:

• If water loss is dominated by evaporation → concentrations trend upward
• If water loss is dominated by drag-out/bleed → concentrations trend downward

Most real lines have both—and the ratio changes with production mix.

❌ Treating evaporation like chemical loss (it’s water loss, concentration goes up)

❌ Not converting weekly events into daily averages
(“We dump 50 gallons sometimes” is meaningless until it’s normalized)

❌ Mixing workload changes with chemistry changes
If surface area processed jumps 2×, drag-out and consumption jump too

❌ Using “standard additions” instead of analysis-driven adds
A schedule is fine as a baseline, but analysis confirms reality

❌ Ignoring drip time + rack orientation
Two operators can have two different drag-out rates with the same parts

1. Log added DI water (A) weekly total
2. Estimate evaporation (E) from idle time or stable weeks
3. Normalize known dumps (B) into gal/day
4. Compute drag-out (D) from the balance
5. Use analysis results to confirm if the math matches reality
6. Implement one drag-out reduction change (drain time, rack angle, drain boards) and see if D drops

Even if you start with a spreadsheet, this data quickly becomes “tribal knowledge” unless it’s built into the system.

In Lab Wizard Cloud, teams can:

• Standardize makeup / replenishment logging
• Tie analysis results and additions to a station history
• Add alerts when results drift or additions become abnormal
• Maintain an audit trail of what happened, who did it, and why

If you want to turn these calculations into repeatable, shift-proof workflows, start with:

• How to Automate Plating Bath Chemistry
• How to Reduce Chemical Waste in Plating Shops
• How to Set Control Limits in Plating Shops
• Lab Wizard Alerts Tutorial