diff --git a/brewery/README.md b/brewery/README.md
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--- a/brewery/README.md
+++ b/brewery/README.md
@@ -16,4 +16,16 @@ p: Carbonization gauge pressure in bar
 
 https://elfring.ms/blog/rpn-karbonisierungsrechner
 
+## GFWtr - Grainfather Water Calculator
+Asks for the batchvolume in l (Aussschlahmenge / Asslg) and grainbill in kg (Malz) and 
+calculates the amount of mash- and sparge-water for grain bills > 4,5 kg according to
+this formula from the Grainfather manual:
+```
+MashWater = GB * 2.7 + 3.5
+SpargeWater = (BV + WL) - MashWater + (GB * 0.8)
+```
+GB: Grainbill in kg  
+BV: Batchvolume in l  
+WL: Waterloss in boil & trub in l (defaults to 5)  
+Adjust waterloss in line 10
 
diff --git a/brewery/gfwtr.raw b/brewery/gfwtr.raw
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diff --git a/brewery/gfwtr.txt b/brewery/gfwtr.txt
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+++ b/brewery/gfwtr.txt
@@ -0,0 +1,25 @@
+00 { 93-Byte Prgm }
+01▸LBL "GFWtr"
+02 INPUT "Asslg l"
+03 INPUT "Malz kg"
+04 2.7
+05 ×
+06 3.5
+07 +
+08 STO 01
+09 RCL "Asslg l"
+10 5
+11 +
+12 RCL 01
+13 -
+14 RCL "Malz kg"
+15 0.8
+16 ×
+17 +
+18 STO 02
+19 "H Guss: "
+20 ARCL 01
+21 ├"[LF]N Guss: "
+22 ARCL 02
+23 AVIEW
+24 END