In case anyone were to be interested in some historical yeast water, here's one from 1806.
Maria Rundell, A New System of Domestic Cookery
To Make Yeast
Thicken two quarts of water with fine flour, about three spoonfuls; boil half an hour, sweeten with near half a pound of brown sugar; when near cold put into it four spoonfuls of fresh yeast in a jug, shake it well together and let it stand one day to ferment near the fire without being covered. There will be a thin liquor on the top, which must be poured off; shake the remainder and cork it up for use. Take always four spoonfuls of the old to ferment the next quantity, keeping it always in succession.
A half-peck loaf will require about a gill.
Spence
Maria Rundell, A New System of Domestic Cookery
To Make Yeast
Thicken two quarts of water with fine flour, about three spoonfuls; boil half an hour, sweeten with near half a pound of brown sugar; when near cold put into it four spoonfuls of fresh yeast in a jug, shake it well together and let it stand one day to ferment near the fire without being covered. There will be a thin liquor on the top, which must be poured off; shake the remainder and cork it up for use. Take always four spoonfuls of the old to ferment the next quantity, keeping it always in succession.
A half-peck loaf will require about a gill.
Spence