Water Quality and Sourdough

Sourdough is mostly water and flour. The water matters more than people think.

The basic problem

Modern municipal water often contains:

• Chlorine — kills bacteria; bad for sourdough cultures
• Chloramine — a longer-lasting chlorine; very bad for sourdough
• Fluoride — generally fine for sourdough, but adds mineral content
• Sodium — varies by region and source
• Calcium — affects gluten development
• Magnesium — affects yeast performance

What matters most

Chlorine and chloramine

Chlorine kills the wild yeast and bacteria in your starter. Chronic exposure leads to weak, sluggish cultures.

Solutions:

• Leave tap water uncovered overnight (chlorine evaporates; chloramine does not)
• Use a carbon filter (removes chlorine, partially removes chloramine)
• Use a reverse osmosis filter (removes everything)
• Use bottled spring water
• Boil for 15 minutes, cool (removes chlorine; partial on chloramine)

If your water tastes like a swimming pool, your starter is suffering.

Hardness

Hard water has high mineral content (calcium, magnesium). It strengthens gluten, slows fermentation slightly, and can sometimes produce slightly tighter crumb.

Soft water (low minerals) ferments faster and produces more open crumb but weaker gluten structure.

Most water is in the middle range and works fine for sourdough.

pH

Tap water in most regions is slightly alkaline (pH 7.0–8.0). This is fine.

Very acidic water (pH < 6.0) inhibits yeast. Very alkaline water (pH > 9.0) is uncommon but would be problematic.

How to test your water

Most municipalities publish annual water quality reports online. Look for:

• Chlorine and chloramine levels
• Hardness (in grains per gallon or ppm)
• pH
• Total dissolved solids (TDS)

A simple TDS meter ($15) gives you a reading instantly.

For pH, basic litmus strips are cheap and accurate enough.

What I recommend

Bare minimum — use room-temperature tap water that's been left uncovered overnight. Removes most chlorine. Free.

Better — use a basic refrigerator filter or pitcher filter (Brita, PUR). Removes chlorine, much of the chloramine, some minerals.

Best for serious bakers — a dedicated kitchen filter with carbon and KDF (removes chlorine, chloramine, and heavy metals). $80–150 installed.

Overkill — reverse osmosis. Strips everything from the water. The bread is no better than with regular filtered water.

Bottled water

Spring water (Poland Spring, Crystal Geyser, etc.) is usually fine for sourdough.

Distilled water lacks the minerals starter needs — works for one bake but if used regularly, slows fermentation.

Mineral water (San Pellegrino, Perrier) has too much mineral content; can affect gluten and yeast.

When water actually matters

For most home bakers, the difference between filtered and unfiltered tap water is small but noticeable over time.

For starters specifically: filter the water. A freshly-built starter that struggles often improves dramatically when you switch from chlorinated tap to filtered water.

For dough: filter is better but tap-with-overnight-rest is fine.

What to do if your bread suddenly stops working

A surprisingly common scenario: your sourdough has been working great for months, then suddenly the starter is sluggish and the bread is dense.

Check:

1. Did your municipal water provider switch from chlorine to chloramine? (Common in summer months in some regions.)
2. Did your filter expire?
3. Did you switch water sources (vacation, new house)?

Water changes can wreck a starter that's been thriving. Worth checking.

Salt and water interaction

Salt in dough is also relevant. The 2% salt typical in sourdough recipes is enough to slow fermentation slightly but not enough to be a problem.

If you're using softened water (sodium-rich from a water softener), reduce your added salt by 0.5%. Otherwise, the bread tastes salty.

Conclusion

Don't overthink it. Filter your starter water; tap is fine for dough water. If your starter is struggling and you can't figure out why, suspect water before you suspect technique.