r/zerowater

Hi y'all — I’m trying to figure out whether this is expected ZeroWater behavior, meter weirdness, or possibly a defective/exhausted filter issue.

I use ZeroWater pitchers in an area with very hard tap water, and risk of PFAS. Lately I’ve noticed the filtered water starts tasting acidic/tart/lemony before the included TDS meter shows anything above 0. Today I tested pH because I wanted to see what was going on.

I calibrated a cheap pH meter with pH 7 and pH 4 buffer solutions. After recalibrating/power cycling, the pH 7 buffer read correctly at 7.0. My raw tap water tested around pH 7.1.

ZeroWater samples tested much lower:

• Fresh ZeroWater from a filter replaced about 2 days ago: ~pH 5.3–5.6
• Older saved ZeroWater sample from a previous filter while TDS still read 0: ~pH 4.3
• Another older ZeroWater sample: ~pH 5.5
• Raw tap water: ~pH 7.1

I know very low-TDS water can be difficult to measure accurately with cheap pH meters, and I know unbuffered water can absorb CO₂ and read acidic. But the taste change is noticeable to me, and the readings are repeating after calibration.

Has anyone else seen ZeroWater produce acidic water while the TDS meter still reads 0? Is this normal for very hard source water, a sign of filter exhaustion before the TDS meter detects it, or possibly a bad filter/batch?

I’ve stopped using straight ZeroWater for drinking for now and contacted Culligan/ZeroWater support, but I’m curious whether others have measured this or noticed the same taste shift.

Thanks.