I think when we dehydrate our bodies then hold onto any morsel of water from veg/fruit/actual water and scream 'im keeping it cos you are going to dehydrate me again' so a couple of days and plenty of water and body will say 'thankyou for rehydrating me all the time you can now wee it out and i wont keep hold of it'. (this is obviously medical terminology!) for example yesterday i probably had about 2-3 litres of water and only went to the toilet 3 times!)
this morning ive had litre of water and 2 coffees and been 4 times.
tmi? probably but there is your explanation from Dr Vicky