Drinking plenty of water is known to ease headaches, boost concentration and aid digestion.
Medics from the US National Heart, Lung and Blood Institute have now revealed staying hydrated may improve our heart health.
The team analysed more than 15,000 adults over 25 years, from midlife to old age.
Those with the highest amounts of sodium in their blood, a measure of hydration, were more likely to develop heart failure – when the organ is unable to pump blood around the body sufficiently – decades later.
Read more: Go plant-based to ward off heart disease
Even a sodium level that is considered to be normal was linked to the cardiovascular complication, prompting the medics to urge people "take action if they drink too little".
"Our study suggests maintaining good hydration can prevent or at least slow down the changes within the heart that lead to heart failure," said study author Dr Natalia Dmitrieva.
"The findings indicate we need to pay attention to the amount of fluid we consume every day and take action if we find we drink too little."
Read more: Your first job influences heart health
The NHS recommends adults consume six to eight glasses of "healthy drinks" a day, with water, milk and unsweetened tea all counting towards the target.
In 2015, Spanish scientists reported only 60% of women and 40% of men meet the official guidelines when it comes to an "adequate intake of water".
A person's "hydration status" can be "precisely measured" via their serum sodium, the amount of salt in their blood.
When someone goes without water, their serum sodium concentration rises. The body then attempts to conserve water, activating processes that have been linked to heart failure.
"It is natural to think hydration and serum sodium should change day to day depending on how much we drink on each day, however, serum sodium concentration remains within a narrow range over long periods, which is likely related to habitual fluid consumption," said Dr Dmitrieva.
Heart failure usually occurs when the organ has become too weak or stiff. The serious condition generally worsens over time, with treatments only able to ease symptoms, like breathlessness and fatigue.
Lifestyle changes – such as eating healthily and exercising regularly – may also ease heart failure, which can severely limit a person's everyday life and eventually be fatal.
Watch: Woman discovers she has heart failure thanks to her pregnancy
The medics analysed the serum concentration of more than 15,000 adults, aged 44 to 66. It was then measured again five times until the participants reached 70 to 90 years old.
The participants were divided into four groups based on their serum sodium level at the first and second measurement, collected in the first three years of the study.
Results – presented at the European Society of Cardiology Congress 2021 – reveal a higher sodium serum concentration in midlife was linked to heart failure when the fifth measurement was taken, 25 years after the start of the research.
Every 1 mmol/l rise in serum sodium was associated with a 11% increased risk of heart failure.
This rise was also found to raise the odds of developing left ventricular hypertrophy by one fifth (20%). Left ventricular hypertrophy occurs when the walls of the left ventricle – the heart's main pumping chamber – thicken, potentially blocking blood flow out of the vital organ.
Watch: Heart failure linked to cancer
Dehydration in midlife was also linked to the participants developing left ventricular hypertrophy down the line.
The risk of developing both left ventricular hypertrophy and heart failure at 70 to 90 years old began to increase when a participant's midlife serum sodium exceeded 142 mmol/l, despite 135 mmol/l to 145 mmol/l being considered normal.
This remained the same after the medics accounted for other factors that influence heart failure risk, like blood pressure, body mass index and smoking status.
"The results suggest good hydration throughout life may decrease the risk of developing left ventricular hypertrophy and heart failure," said Dr Dmitrieva.
"In addition, our finding that serum sodium exceeding 142 mmol/l increases the risk of adverse effects in the heart may help to identify people who could benefit from an evaluation of their hydration level.
"This sodium level is within the normal range and would not be labelled as abnormal in lab test results, but could be used by physicians during regular physical exams to identify people whose usual fluid intake should be assessed."