White chunks in urine

Hi - I'm on day 5 of a water fast. I've been having 1 thin slice of lemon in warm water throughout the day (same slice for all day) and had a 1/2 bottle of pelligrino on day 3 because I didn't think I was going to make it :-/ the rest has been room temperature water - probably about 3-4 liters a day - but I usually drink 2-3 at least, so not really a huge overload.

Today I have had chunks in my urine 3 times today and I'm a little concerned. I've only had this 2x in the past when I did a really heavy/long work out.

Has anyone else seen this or experienced this in the past? I'm not really hungry and think I can make it to my 10 day goal - but worried about the material in my otherwise fairly clear urine....

Thanks in advance for any info!