Use distilled water to prevent leaving residue.
I drain the water everyday.
Three days is OK,
seven days is OK.
Once you take it out of the water,
you must dry it pretty quickly
before it molds.
Do a small batch, of one or two buds.
You are removing the chlorophyl,
which is water soluble,
and thats why the water turns green.
I think water cure takes out too much flavor,
if you have good tasting weed.
I like the jar cure better.
.