I walked the whole VDLP from Sevilla last September/October and saw very very few fountains with potable water.
When you get to the albergue in Cañaveral, be sure to explicitly ask about the path to Galisteo. They did not mention a long term closure and a number of people walking on the same day were confused by conflicting information.
Actually, one of our worst days for water was shortly after Cañaveral in the stage from Galisteo to Cáparra. After much consideration, I shared a bit of my emergency reserve of water with my walking partner (only because he was quite adept at getting us complementary Orujos after dinner). On longer stages, I found that my 1.5 Litre Nalgene bottle and a 500ml back-up was adequate, on shorter stages I did not necessarily fill up the back-up - of course, there are a number of factors which could impact your water consumption.
But actually, my most important advice is if anybody in Valverde de Valdelacasa offers you Morcilla, run do not walk to Fuenterroble de Salvatierra.