Can Water Lower Blood Sugar? What the Evidence Says

Can water lower blood sugar? Staying well hydrated may offer modest support for blood glucose regulation, primarily by helping the kidneys excrete excess sugar and maintaining healthy blood volume. While water is not a treatment for diabetes or hyperglycaemia, evidence consistently suggests that good hydration is a safe, practical component of blood glucose management. This article explores the physiological mechanisms behind hydration and blood sugar, what the clinical evidence shows, how much water to drink if you have high blood sugar, and when to seek medical advice.

Can drinking water actually lower your blood sugar levels?

Water offers modest, supportive benefits for blood glucose by aiding renal glucose excretion and maintaining hydration, but it is not a treatment for diabetes and cannot replace prescribed medication or medical supervision.

Drinking water may help support healthy blood glucose levels, primarily by restoring hydration and supporting the kidneys in excreting excess sugar through urine. The effect is modest and supportive rather than therapeutic, and the precise magnitude is not firmly established by clinical trial evidence. Water is not a treatment for diabetes or hyperglycaemia, and it cannot replace prescribed medication, dietary changes, or medical supervision. However, staying well hydrated is a safe, accessible and evidence-consistent way to support blood glucose regulation as part of a broader management plan.

When blood glucose rises, the kidneys work harder to filter and excrete the excess sugar. This process requires adequate fluid. If a person is dehydrated, the kidneys are less efficient at this task, and blood glucose can remain elevated for longer. Drinking water supports this renal clearance mechanism without introducing additional calories or carbohydrates.

People with type 2 diabetes, prediabetes, or those managing their weight should view good hydration as one component of a healthy lifestyle, alongside balanced nutrition, physical activity, and any prescribed treatment. Water alone will not bring dangerously high blood sugar under control, and anyone experiencing symptoms of hyperglycaemia should seek appropriate medical advice rather than relying on fluid intake alone.

A note on overhydration: drinking very large volumes of water rapidly is not recommended and can, in rare cases, cause low sodium levels (hyponatraemia), particularly in older adults or those with kidney or heart conditions. People with conditions that require fluid restriction should follow the limits agreed with their clinician.

How does staying hydrated affect blood glucose in the body?

Hydration supports blood glucose regulation by reducing vasopressin release, promoting renal glucose excretion via glycosuria, restoring normal blood volume, and helping distinguish thirst from hunger to prevent unnecessary carbohydrate intake.

Adequate hydration supports blood glucose regulation through several physiological mechanisms. One of the most studied involves the hormone vasopressin (also called antidiuretic hormone). When the body is dehydrated, the pituitary gland releases more vasopressin. Observational and experimental research has associated elevated vasopressin levels with increased hepatic glucose production and higher blood glucose concentrations, suggesting that even mild dehydration may contribute to raised blood sugar, though this relationship is associative rather than definitively causal.

The kidneys also play a central role. Under normal conditions, the kidneys begin to excrete glucose in the urine when blood glucose exceeds a threshold of approximately 10 mmol/L, a process known as glycosuria.^[5] This threshold varies between individuals and may be lower in pregnancy, older adults, or those with kidney disease.^[6][7] Sufficient fluid intake supports urine production and therefore helps the kidneys clear glucose more effectively. Conversely, dehydration reduces urine output, limiting this natural clearance pathway.

Blood volume is a further consideration. When fluid intake is low, blood becomes more concentrated, meaning the same amount of glucose is dissolved in a smaller volume of plasma. This raises the measured blood glucose concentration without any additional glucose entering the bloodstream. Rehydrating restores normal blood volume and can therefore reduce a blood glucose reading, though this is a relatively minor effect and should not be interpreted as a clinically meaningful glucose-lowering intervention on its own.

Finally, thirst and hunger signals can overlap. People who are mildly dehydrated sometimes interpret thirst as hunger and consume additional carbohydrates, which raises blood glucose further. Maintaining good hydration habits may help reduce unnecessary snacking and support more stable glucose levels throughout the day.

What does the evidence say about water and diabetes management?

Observational evidence, including the D.E.S.I.R. cohort study, links higher plain water intake with lower risk of hyperglycaemia, though causality is not firmly established; replacing sugary drinks with water is a practical, evidence-consistent step.

Observational research suggests that higher plain water intake is associated with a lower risk of developing type 2 diabetes and with better glycaemic control in people who already have the condition.^[4][8] A prospective cohort study (the D.E.S.I.R. study, published in Diabetes Care) found that adults with higher plain water consumption had a lower risk of developing hyperglycaemia over a nine-year follow-up period compared with those who drank less.^[4] Researchers proposed that the vasopressin pathway was a plausible biological explanation for this association.

It is important to note that most of the available evidence is observational rather than from randomised controlled trials, which means causality cannot be firmly established. People who drink more water may also have other healthy lifestyle habits that independently reduce diabetes risk. NICE guidance on type 2 diabetes management (NG28) emphasises lifestyle modification, including dietary changes and physical activity, as foundational strategies. Adequate hydration is consistent with these recommendations, though water intake is not specifically quantified as a standalone intervention in NICE guidance.

What the evidence does consistently support is that sugary drinks, including fruit juices, fizzy drinks and sweetened teas, raise blood glucose and should be limited or avoided by people with diabetes or prediabetes. Replacing these with plain water is a practical, evidence-consistent step that reduces sugar intake and supports hydration simultaneously. NHS guidance recommends water, plain milk, or unsweetened tea and coffee as the preferred choices for people managing blood glucose.^[2] The overall picture is one of water being a helpful, low-risk component of diabetes management rather than a standalone treatment.

How much water should you drink if you have high blood sugar?

Adults should aim for 1.5 to 2.0 litres of fluid daily, with plain water preferred; people with diabetes may need more during periods of elevated blood glucose due to increased urinary fluid losses.

The NHS recommends that adults aim to drink approximately 6 to 8 cups or glasses of fluid per day, equivalent to roughly 1.5 to 2.0 litres, with plain water being the preferred choice (NHS Live Well: Water, drinks and your health). For people with high blood sugar or diabetes, this general guidance remains appropriate, though individual needs vary depending on body size, physical activity, climate, and any coexisting medical conditions such as kidney disease or heart failure, which may require fluid restriction.

People with diabetes may have higher fluid requirements during periods of elevated blood glucose, because the kidneys excrete more water alongside glucose in the urine, increasing the risk of dehydration. Symptoms of dehydration in this context can include increased thirst, dry mouth, darker urine, fatigue, and headache. These symptoms can overlap with those of hyperglycaemia itself, so monitoring both fluid intake and blood glucose is helpful.

Practical tips for maintaining good hydration include:

• Carry a reusable water bottle and sip throughout the day rather than drinking large amounts infrequently.

• Choose plain water or unsweetened drinks rather than fruit juices, energy drinks or sweetened squashes, which raise blood glucose.

• Monitor urine colour as a simple hydration guide: pale straw yellow indicates adequate hydration, while dark yellow suggests more fluid is needed (NHS: Dehydration).^[1]

• Adjust intake during exercise or hot weather, when fluid losses increase.

Avoid drinking very large volumes of water in a short period, as this can cause hyponatraemia (low blood sodium), particularly in older adults or those with kidney or heart conditions. People with kidney disease, heart failure, or other conditions affecting fluid balance should discuss their individual fluid targets with their GP or specialist before making significant changes to their intake.

When should you speak to your GP about your blood sugar levels?

See your GP if you have persistent symptoms such as increased thirst, frequent urination, fatigue, or blurred vision; contact NHS 111 urgently for vomiting, rapid breathing, or confusion, and call 999 if someone is unresponsive.

You should speak to your GP if you have persistent symptoms that may suggest high blood sugar, including increased thirst, frequent urination, unexplained fatigue, blurred vision, slow wound healing, or recurrent infections. These symptoms can indicate prediabetes or type 2 diabetes, both of which benefit from early diagnosis and structured management. NICE guidance (NG28) supports early intervention to reduce the risk of long-term complications, and your GP can arrange appropriate blood tests to assess your glucose levels and overall risk.^[3]

If you have already been diagnosed with diabetes and your blood glucose readings are consistently outside your agreed target range despite following your management plan, this warrants a review with your GP or diabetes care team. Similarly, if you are making lifestyle changes such as increasing water intake, adjusting your diet, or starting a new exercise routine, your GP can help you monitor the effect on your glucose levels and adjust any medication if needed.

Contact NHS 111 for urgent advice if you experience symptoms of severe hyperglycaemia, such as vomiting, rapid breathing, confusion, or fruity-smelling breath, as these may indicate diabetic ketoacidosis (DKA), which requires prompt assessment. Older adults with very high blood glucose, severe dehydration, and confusion may be experiencing hyperosmolar hyperglycaemic state (HHS), which also requires urgent medical attention. Call 999 or go to A&E immediately if you or someone else loses consciousness or is unresponsive.

For people exploring structured weight management as part of blood glucose control, a range of options exists, including NHS referral pathways and regulated online services. Bolt Pharmacy is a GPhC-registered UK online pharmacy offering online weight-management consultations, with prescriber review and pharmacist support, where clinically appropriate treatment options may be considered following consultation. Suspected side effects from any prescribed medicine can be reported to the MHRA via the Yellow Card scheme at yellowcard.mhra.gov.uk.

Scientific References

1. Dehydration.
2. Water, drinks and hydration.
3. Type 2 diabetes in adults: management (NG28).
4. Low water intake and risk for new-onset hyperglycemia (D.E.S.I.R. study).
5. Mixed-effects modelling to quantify the effect of empagliflozin on renal glucose reabsorption in patients with type 2 diabetes.
6. Impaired decline in renal threshold for glucose during pregnancy.
7. Diabetes in pregnancy: management from preconception to the postnatal period (NG3).
8. Plain-water intake and risk of type 2 diabetes in US adults.
9. Diabetes insipidus — Causes.

Frequently Asked Questions