Still not clear on "drinking to thirst"

On Round 1 of my fasting cycle ( 180 days of fasting) I focused on drinking to thirst. In looking over my journal I realized that I average 2-3 ounces of water per day. I was weak and lightheaded the whole time of the WF.
I am thinking that either I do not know what thirst is or I do not get thirsty very much.
I am on heading into Round 2 WF and have decided to make sure to take in 1.5-2 litres daily to ensure I get enough water. I am hoping that with that amount of water I will not be weak and will be able to at least take daily walk and comfortably be out of bed.
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