FDI P2131, Technical Manual, Page: 61 / 161

3.4.1 Testing Total Dissolved Solids (TDS)
Using the Handheld TDS Meter, test the SWS outlet water stream every time the WRS is refilled
(e.g., every 14 days or 100 cycles, whichever occurs first). Follow the instructions below.
Cartridge Replacement Criteria: If SWS outlet water TDS is ≥ 15 ppm, replace the SWS DI Water
Cartridge. If the TDS reading is < 15 ppm, the SWS can be used as normal.
NOTE: If the feedwater is of poor quality and has a high TDS level, a brand ‐ new cartridge
may result in a TDS reading of greater than 15 ppm. To improve the TDS reading:
1. Improve incoming water quality.
2. Use SWS’s in series to lower the TDS level before filling WRS.
3. Using a collection bucket or Jerry can, reprocess the water twice through the SWS
before filling the WRS
NOTE: The meter is not water ‐ tight. Do not dip the meter beyond the water level limit.
TDS Handheld Meter Calibration Check (every 6 months):
Immerse the meter into distilled water and verify it reads ≤ 5 ppm. If it reads > 5 ppm, either the
distilled water could be contaminated, or TDS Meter is out of calibration and should be replaced.
Taking a TDS Measurement:
1. Remove the protective cap.
2. Turn the TDS Meter ON.
3. Collect a sample of SWS outlet water in a clean container.
4. Immerse the Meter into the sample up to the Water Level Limit.
5. Lightly stir the Meter in the water to dislodge any air bubbles.
6. Wait until the reading stabilizes and then press the HOLD button. The value displayed is
the TDS Level of the water.
NOTE: Be sure to turn the TDS Meter OFF before storage to preserve the battery.
3.4.2 SWS Deionized Water Cartridge Capacity
The amount of deionized water that the SWS can produce depends on the concentration of Total
Dissolved Solids (TDS) of the supply water. For example, very hard water might have 425 ppm
TDS, while relatively soft water might have 50 ppm TDS. The table below shows the approximate
capacity in gallons of deionized water that the SWS can produce for varying supply water TDS
levels.

Soft

Hard

Very Hard

Supply Water TDS (ppm) 0 50 120 255 425
SWS Capacity until Cartridge replacement (Gal) 1850 633 264 124 74
Handheld TDS Meter
P/N: P2131 ‐ 3 ‐ 9010
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