Brewing Water Basics

Water is the easiest ingredient to ignore and surprisingly powerful once you understand it. The minerals in it shape mash enzyme activity, how 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.

Start with your own water, not someone else’s numbers. Members are spread across the Hutt and Wellington and are not all in the same situation: most are on reticulated supply, some are on a bore or tank, and on a group brew day you are using whatever comes out of the host’s tap. The principles below are universal; the salt amounts assume a soft, low-mineral starting point, which covers most but not all of us.

Start by removing chlorine

Reticulated water is treated with chlorine or chloramine. Both react with malt to produce the plaster and TCP fault (chlorophenols), and the detection threshold is in parts per billion.

Campden (metabisulphite) at one crushed tablet per 75 L, in all brewing water — mash and sparge. Half a tablet covers roughly 38 L, which is about right for a single 23 L batch’s total. Stir, wait a couple of minutes.

Why that is not what your packet says

Pick up a tin of Campden tablets and the instructions will say something like one tablet per 4.5 L. That is not a misprint, and it does not mean the figure above is wrong — the two numbers are for different jobs.

Those packet instructions are for sanitising fruit must and preserving wine or cider. That job needs a lasting SO₂ residual, around 50 ppm, to suppress wild yeast and act as an antioxidant in a product that will sit for months.

Dechlorinating brewing water is not that job. You only need enough metabisulphite to reduce the chlorine actually present, which in a reticulated supply is roughly 0.5–1.5 ppm.

A typical tablet is about 0.44 g of metabisulphite, roughly 57% SO₂ by weight, so around 253 mg of SO₂ per tablet. Spread through 75 L that is comfortably more than enough to deal with a 1.5 ppm chloramine residual, with margin to spare.

Do not use the packet dose on brewing liquor. It is roughly sixteen times what dechlorination needs, and excess sulphite can read as burnt match in the finished beer and is not doing your yeast any favours either.

Do check your packet for one thing: tablet mass and which salt it is (sodium or potassium metabisulphite). Most are close to 0.44 g, but brands vary, and if yours is noticeably heavier or lighter, scale accordingly.

This step matters more than any mineral addition. Boiling is not a substitute — it drives off free chlorine reasonably well and does essentially nothing to chloramine. If you get the fault anyway, Bandaid, TCP & Clove works through every other route it takes.

If you are on tank or bore water, you have no residual to remove and can usually skip campden — right up until someone shock-chlorinates the tank, which is normal maintenance and easy to forget. Bore water is also often much harder than the regional supply, so the salt additions below may be wrong for you in the other direction. Get an analysis before you trust any of these numbers.

What each ion does

The one lever that matters most

Most of the flavour effect comes down to the sulfate-to-chloride ratio:

• ~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

If you change nothing else, change this.

The Waiwhetu aquifer — our local water

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 through a short stretch of riverbed at Taita Gorge, and the water takes years to filter down the valley through alluvial gravels before it is drawn at Waterloo.

Wellington Water publishes the analysis. These are the brewing-relevant figures:

Magnesium and sodium are not published in that analysis. Both are low here, but if you want real numbers you will need your own test.

Two caveats on reading those figures. The Gear Island sulfate row is labelled sulphite on the published table — almost certainly a typo, since the value matches Waterloo’s sulfate figure to two decimal places and carries the same guideline value. And several of these rows rest on only one or two samples, so treat them as the right order of magnitude rather than precise.

Gear Island is the better guide for brewing, because it is the least-processed. Waterloo aerates the water to strip CO₂ and adds lime to raise pH and alkalinity, so its figures describe treated water rather than what is in the ground.

What this means at the mash tun

The regional water gets described as “soft”, and by hardness it is. But soft is not the same as low-alkalinity, and that distinction is where people come unstuck here.

Calcium around 18 mg/L is well under the 50 ppm minimum you want for mash enzyme health and yeast flocculation. Meanwhile alkalinity at ~48 as CaCO₃ — roughly 59 mg/L bicarbonate — is enough to push back on your mash pH. Pilsen water, the classic blank slate, sits well below that.

So the practical picture is low calcium and moderate buffering, which means:

• Almost every beer wants calcium added. Gypsum or calcium chloride depending on the style
• Pale beers will run high on mash pH if you treat this as a blank slate. Expect to need acid, or acidulated malt, on pale grists — measure rather than assume
• Dark beers are the easy case. Roast malt acidity and this alkalinity partly cancel

Residual chlorine is not constant. It rises after mains flushing, reservoir work and heavy rain, and generally through summer. A marginal campden dose that works most of the year gets caught out when the network shifts.

The artesian taps

Two public taps in the valley draw the aquifer directly, and some members brew with them:

• Te Puna Wai Ora, Buick Street at the Jackson Street junction, Petone — a sculpture by Louise Purvis, installed 2003
• Dowse Square, Lower Hutt, outside the Dowse Art Museum — installed 2012

Both draw the same Waiwhetu aquifer, so the profile above is your starting point for either. Both are UV-treated on site — that was added after E. coli was detected in 2017 — but neither is chlorinated.

What that means for brewing:

• No campden needed. There is no chlorine or chloramine to neutralise, which removes the single most common cause of the plaster and TCP fault. This is the real attraction
• It is still not a blank slate. Same calcium and alkalinity picture as above — arguably more so, since it has not been through Waterloo’s aeration. Treat it as low-calcium, moderate-alkalinity water and build from there
• It is raw water with a UV step, not sterile water. Fine on the hot side, where it is about to boil. Do not use it untreated for topping up finished beer, rinsing sanitised gear or making up sanitiser — use RO or campden-treated tap water for those, as covered in Bandaid, TCP & Clove
• Collect into clean, sanitised vessels and use it promptly. Unchlorinated water sitting warm in a drum for a fortnight is not the same water you collected

Hauling 40 L across town is a real cost for a benefit you can also get from a campden tablet. It is worth it if you like the idea, or if you want one variable removed while chasing a fault — not something to feel obliged to do.

The common salts

Acidulated malt is the other pH lever — easier to dose than acid if you are not confident with a pipette, at 1–2% of the grist.

Worked targets (per 23 L, from soft water)

• West Coast IPA / pale ale — ~CaSO₄ 6 g + CaCl₂ 2 g + MgSO₄ 2 g (≈2.5–3 : 1 sulfate:chloride)
• Hazy / NEIPA — ~CaCl₂ 4 g + CaSO₄ 2 g, chloride-forward
• Belgian / saison — ~CaSO₄ 3 g + CaCl₂ 2 g. Let the yeast lead
• Lager / pilsner — very soft, low sulfate: ~CaCl₂ 1–2 g, or nothing at all

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

Mash pH — the payoff

Mash enzymes work best in a tight band:

• 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, where the roast malt drops pH on its own

How to do it. Add salts to the strike water before heating. Five to ten minutes after mashing in, once the 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, re-check. On soft water with a pale grist, 1–2 mL usually does it.

Adjust early. Corrections after the 30-minute mark do very little.

Keep sparge water at pH 5.4–5.6 as well. Sparging hot at high pH pulls tannins out of the husks, which is one of the two things most often mistaken for a phenolic fault.

If you share a brew day

Two things go wrong when several people brew on one supply:

• Everyone assumes someone else treated the water. Agree who is dosing campden, and dose the whole volume once rather than per-brewer
• One shared bucket of untreated water used for topping up or making sanitiser faults every batch on the day, not just one

Quick checklist

• Campden in all water, at one crushed tablet per 75 L
• Salts weighed on a 0.1 g scale, not guessed
• Salts split appropriately between mash and sparge
• Mash pH checked at 5–10 minutes, corrected with lactic acid if high
• pH meter calibrated with fresh buffer; probe stored in storage solution
• Sparge water pH 5.4–5.6

Common issues

• Mash pH too high on a pale beer — salts alone were not enough buffer; add lactic acid in 1 mL steps
• Harsh, astringent bitterness — too much sulfate (above ~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 or TCP flavour — chlorine not neutralised. See Bandaid, TCP & Clove

See also: Cleaning & Sanitation, and the brew-day walkthrough for where water treatment sits in the day.