Tools
Two things to do the sums for you.
Both run entirely in your browser. What you type is not sent to us or to anyone else, and nothing is saved. Each tool shows the rule it applies and where the rule comes from, and stays silent where the sources give no number.
Tool 1
Batch calculator
Tell it how much rice you want to use and which method. It gives the water to add, roughly how much rice water you'll get, and how many ice cubes that fills, for the cube size of your tray.
Uses only the ratios in this site's three recipes.
Open the calculator →
Tool 2
Made on → use by
Enter when you strained your batch and where you're keeping it. It gives the time it needs to be chilled by and, for the fridge, a use-by time. For the freezer and for fermented batches it explains why it gives no date.
Rules borrowed from FDA and UK Food Standards Agency food guidance. A rule of thumb, not a tested shelf life.
Open the helper →
Why these two
The questions we see most are practical: how much water for the rice I have, how many cubes will that make, and how long can I keep it. The first is arithmetic on our own recipes. The second has no tested answer for rice water, so the helper applies the most cautious official food rules we could verify and labels them as borrowed. The reasoning is on the safety page, and the sources are in the evidence register.
Neither tool knows anything about your skin. Patch test first; the method is on the safety page.