Brewing Water Basics

Water is the ingredient that is easiest to ignore and surprisingly powerful once you understand it. The minerals dissolved in it shape mash enzyme activity, how hop bitterness comes across, how full the malt tastes, and yeast health. You do not need a chemistry degree — you need a few ions, one ratio, and a target pH.

This guide is worked from the Waiwhetu aquifer water that supplies the Hutt Valley and much of Wellington. The principles are universal; the specific salt amounts assume a soft, low-mineral starting point. Start from your own water report if you are on a different supply, a bore or a tank.

Start by removing chlorine

Tap water is treated with chlorine or chloramine. Both react with malt to produce a plaster / band-aid off-flavour (chlorophenols). Neutralise them first: add campden (metabisulphite) at one crushed tablet per 75 L to all brewing water — half a tablet covers roughly 38 L, about right for a 23 L batch’s total. Stir, and wait a couple of minutes. This step matters more than any mineral addition.

Ignore the dose on the packet

The tin will say roughly one tablet per 4.5 L, and that is not a misprint — it is the dose for sanitising fruit must and preserving wine or cider, which needs a lasting SO₂ residual around 50 ppm to suppress wild yeast and act as an antioxidant.

Dechlorinating brewing water is a different job. You only need enough to reduce the 0.5–1.5 ppm of chlorine actually present.

A typical tablet is ~0.44 g of metabisulphite at roughly 57% SO₂ by weight, so ~253 mg of SO₂. Across 75 L that clears a 1.5 ppm chloramine residual with margin. The packet dose is about sixteen times what is needed, and surplus sulphite reads as burnt match — see Bandaid, Medicinal & Plastic.

The one thing worth reading off the packet is the tablet mass and which salt it is (sodium or potassium metabisulphite). Most sit near 0.44 g; scale if yours differs.

What each ion does

The one lever that matters most: sulfate-to-chloride ratio

You can get a long way by thinking in terms of the SO₄ : Cl ratio, which tilts the beer’s balance:

• ~2–3 : 1 (sulfate-forward) → crisp, dry, bitter. West Coast IPA, pale ale.
• ~1 : 1 → balanced.
• ~1 : 2 (chloride-forward) → soft, round, full. Hazy IPA, malty styles.

The local starting point: the Waiwhetu aquifer

Around 40% of the drinking water for Lower Hutt and Wellington comes from the Waiwhetu aquifer, a buried gravel layer running under the Hutt Valley and out beneath the harbour. It is recharged from the Hutt River at Taita Gorge and takes over a year to filter down the valley before it is drawn.

Tiaki Wai (formerly Wellington Water) publish the analysis per treatment plant. The brewing-relevant figures, with the number of samples behind each:

Magnesium and sodium are not published. Use the Gear Island column: Waterloo doses lime to lift alkalinity, which is calcium hydroxide and inflates its own calcium reading, while Gear Island doses caustic soda and leaves calcium alone. For the same reason, never read sodium off Gear Island.

Soft is not the same as low-alkalinity

This water gets called soft, and by hardness it is — but it is not a Pilsen-style blank slate, and that is the trap. Pilsen sits near 17 ppm bicarbonate; this is nearer 59. So the real picture is low calcium with moderate buffering:

• Almost every beer wants calcium added. 18 ppm is well under the 50 ppm minimum for mash enzyme health and yeast flocculation
• Pale beers will run high on mash pH. Expect to need lactic acid or acidulated malt on a pale grist — measure rather than assume
• Dark beers are the easy case. Roast malt acidity and this alkalinity partly cancel

The artesian taps

Two public taps draw the aquifer directly: Te Puna Wai Ora on Buick Street at the Jackson Street junction in Petone, and Dowse Square in Lower Hutt. Both get on-site filtration and UV, and neither is chlorinated — when permanent chlorination of the Lower Hutt supply came in during April 2017, the fountains were exempted and given their own treatment instead.

No campden needed on tap-drawn water, which is the main reason to bother hauling it. Two caveats. It is raw water with a UV step rather than sterile water, so it is fine on the hot side where it is about to boil, but do not use it untreated for topping up finished beer or making up sanitiser. And the taps get no aeration and no alkali dosing, so the real alkalinity and pH are very likely lower than the 48 and 7.7 in the table — treat those as a ceiling, and expect to need less acid rather than more.

Calcium, chloride and sulfate carry across from the table unchanged; filtration and UV do nothing to them.

Figures from Tiaki Wai’s published per-plant analysis, accessed 2026-08-14: What’s in your water · treatment plants · chlorination. There is no published analysis for the two taps specifically — they are not sampled as their own supply — so any precise-looking number for either is a model, not a measurement.

The common salts

Worked targets (per 23 L, from the aquifer)

Worked from the Gear Island baseline above — Ca 18, SO₄ 6.4, Cl 16. Gypsum here means CaSO₄·2H₂O and calcium chloride means CaCl₂·2H₂O; if yours is anhydrous calcium chloride rather than dihydrate flakes, use about 25% less.

Every row clears the 50 ppm calcium floor, which is the other job these salts are doing besides setting the balance.

No Epsom salt in any of them. Malt supplies ample magnesium for yeast health, and on this water Epsom’s only other effect is adding sulfate you have already set deliberately with the gypsum — it moves your ratio without you asking it to.

Dial these in with a calculator (Brewfather, Bru’n Water) against your own water report — these are starting points, not gospel.

Mash pH — the payoff

Mash enzymes work best in a tight pH band. Aim for:

• 5.2–5.4 for pale and hoppy ales
• 5.3–5.5 for malty and Belgian beers
• 5.4–5.6 for dark, roasty beers (the roast malt drops pH on its own)

How to do it: add your salts to the strike water before heating. Five to ten minutes after mashing in (once temperature is stable), read the mash with a calibrated pH meter. If a pale beer reads above ~5.5, add lactic acid 1 mL at a time, stir, wait 5 minutes, and re-check. On soft Wellington water with a pale grist, 1–2 mL usually does it. Adjust early — corrections after the 30-minute mark do little.

Keep sparge water around pH 5.4–5.6 too: sparging hot (75–78 °C) at high pH risks pulling tannins (astringency) out of the husks.

Quick checklist

• Campden added to all water (chlorine/chloramine gone)
• Salts weighed on a 0.1 g scale (don’t guess)
• Salts split appropriately between mash and sparge
• Mash pH checked at 5–10 min, corrected with lactic acid if high
• pH meter calibrated with fresh buffer, probe stored in storage solution

Common issues

• Mash pH too high (pale beer) — salts alone weren’t enough buffer; add lactic acid in 1 mL steps.
• Harsh, astringent bitterness — too much sulfate (>250 ppm) or tannin from a hot, high-pH sparge; cut the gypsum and treat the sparge water.
• Thin, flat finish — not enough chloride; add 1–2 g CaCl₂.
• Plaster / band-aid flavour — chlorine/chloramine not neutralised; campden next time.