How much water do we really need?

Q: Is there any truth to the claim that we need to drink eight glasses of water a day? Regards, George

A: Hi George. Hydration is such an important topic and the impact that this can have on how we look, think and feel is far too often underestimated. Dehydration impairs physical and mental performance, and even slight dehydration can leave us feeling fatigued.

The idea that everyone requires exactly eight glasses of water a day doesn’t really make sense to me, as we’re all different so we will have different needs. Science currently tells us we require 33 millilitres of fluid per kilogram of body weight, so a person weighing 70kg would need around 2.3 litres per day.

However, this is really still just an estimate, as how much fluid we require will depend on the climate and how active we are. Caffeinated and alcoholic beverages are diuretics and drag water out of the body so you may need more water if you consume these on a regular basis.

As a general guide, most adults will need between two and three

litres of fluid a day. Eight glasses of water would put you at the lower end of this range.However, we also obtain some fluid from non-starchy vegetables, soups and other drinks such as herbal teas.

If you would like to have a number of glasses to aim for each day, eight glasses is probably a good starting point, but I encourage you to tune in to your body’s thirst signals and be guided by this. After all, thirst is the body’s way of signalling to you that it requires water.

Q: I’ve been told that my total body water ranges between 56-58 per cent. What should my total body water be and how do I know if I’m retaining too much fluid? Kindest, Jennifer

A: Hi Jennifer. Percentage body water can vary depending on a number factors, such as age, gender and level of muscle mass. It can be anywhere from 45 to 70 per cent of body weight but for adults, it is typically between 50 to 60 per cent.

Without knowing how your total body water was measured it’s difficult to comment on this, but I encourage you to reflect on the level of accuracy that can be obtained when measuring your body composition outside a laboratory setting. Rather than looking to a measurement, I cannot encourage you enough to simply bring awareness to your body and any signs or symptoms that may indicate dehydration or fluid retention.

A measurement of total body water doesn’t tell us the full picture, as it doesn’t indicate where the fluid actually is in the body (how much is inside our cells, between and around the cells and in the blood and lymph). Fluid accumulating outside the cells is what can lead to feelings of fluid retention, such as feeling ‘‘puffy’’ or feeling your clothes dig in as the day progresses. Swollen ankles can also be a sign of fluid retention.

Many women experience fluid retention at certain stages of their menstrual cycle, due to an imbalance in oestrogen and progesterone. However, fluid retention can also be driven by sub-optimal liver function, mineral deficiencies or imbalances, and/or poor lymphatic flow.

❚ Dr Libby is a nutritional biochemist, best-selling author and speaker. The advice contained in this column is not intended to be a substitute for direct, personalised advice from a health professional. Join Dr Libby in Christchurch for one weekend to change your life: November 25 and 26. More info at drlibby.com

123RF Thirst is the body’s way of signalling to you that it requires water.