I don't carry a sponge but I have carried clean cloths of various types for the purpose of collecting dew.

Once in dry season in Brazil I "stranded" myself on an "island", a dry ridge with no flowing water. I was forced to use expedient means to collect water from the "island".

I used a solar still, transpiration bags, and dew collection. By far the dew collection paid off the best and made the other two methods seem like a waste of time. The solar still and transpiration bags collected a few ounces of water combined. Collecting dew I was able to produce a liter and half in about an hour. Much of that was very clean water collected from my tent surface. The water collected from the wet grass was very muddy looking and needed to be filtered twice. Dew collection is worth packing a sponge for. It paid off very well for me. At other times in the same location very little dew was formed.

On that trip I carried plenty of water to measure my requirements compared to what I was able to collect. I drank as I felt necessary. I judged myself to have survived. If I had needed to stay longer I would have risen pre-dawn and collected dew for several hours each day for a total collection of three liters per day. That was what I drank of the water I brought with me to the "island". It would have been fairly easy to do. Mac