The bladder is a hollow, elastic muscular organ in which urine is stored
until it is passed out of the body via the urethra. The bladder is found in
the pelvis behind the pelvic bone and can expand and hold around 400
– 600ml of urine at a time, for up to five hours.

The more fluid that is drunk, the more urine is produced. When the body
becomes hot, and sweat is produced, less urine will be made. Of the
urine produced, around 96% of it is water, but it also contains waste
salts and a substance called urea, which is made during the breakdown
of proteins in the liver. It is a transparent solution but is amber in colour.

The sweat that the body produces may also contain urea and it is
essential that this does not build up in the body as it can be an indicator
that the kidneys are not working satisfactorily.