Why hydration is different in CKD
Healthy kidneys adjust water excretion minute-by-minute — drink more, urinate more. In CKD this regulation gets less precise. In early CKD it still works well. In later CKD, the kidneys lose the ability to concentrate or dilute urine, so people can become dehydrated more easily and also retain fluid more easily.
Once dialysis starts, urine output usually falls progressively. At that point fluid intake has to match what the kidneys can no longer remove — otherwise fluid builds up between dialysis sessions and causes high blood pressure, ankle/lung swelling and heart strain.
What 'enough' looks like at each CKD stage
- CKD 1–2 (eGFR ≥ 60): drink to thirst, aim for 1.5–2 L total fluid/day, more if exercising or in hot weather. No special restriction.
- CKD 3 (eGFR 30–59): same as above for most people. Avoid prolonged dehydration (long-haul flights, heatwaves, heavy exercise without replacement).
- CKD 4 (eGFR 15–29): usually 1.5–2 L, but starting to be individualised — if blood pressure or ankle swelling is becoming a problem your team may suggest less.
- CKD 5 not on dialysis (eGFR < 15): individualised — your renal team will set a target based on urine output, BP and oedema.
- Haemodialysis: typically 500 ml + (24-hour urine output) = total fluid/day. Includes tea, coffee, soup, ice, juicy fruits.
- Peritoneal dialysis (PD): less restrictive — daily dialysis usually allows more flexibility, but still individualised.
Does drinking more water slow CKD?
Short answer: no — for most CKD patients, drinking extra water beyond thirst does not slow kidney decline.
The definitive trial was the CKD WIT (Water Intake Trial), published in JAMA 2018. 631 adults with CKD stage 3 were randomised to drink an extra 1.0–1.5 L water daily or to maintain usual intake. After 1 year there was NO difference in eGFR decline.
The one clear exception is kidney-stone disease — if you've had stones, higher fluid intake (enough to make > 2 L urine/day) approximately halves recurrence over 5 years.
The practical advice: stay well-hydrated, don't force water, and don't expect litres of extra water to 'flush' your kidneys.
Kidney Vitality is a daily multivitamin developed by a UK Consultant Nephrologist using renal nutrition principles. It contains no added potassium, magnesium, phosphorus or iron, and no herbal blends. See the formulation.
Fluid restriction on dialysis — what counts
If you're on a fluid restriction (typical haemodialysis target: 500 ml + urine output), everything liquid at room temperature counts:
- Water, tea, coffee, squash, fizzy drinks, milk, juice — yes
- Soup, gravy, sauces — yes
- Ice cubes, ice lollies — yes (a typical ice cube is ~ 25 ml)
- Jelly, yoghurt, custard — partially count (your dietitian will guide)
- Juicy fruits (melon, oranges) — contribute, count partially
Tips for managing thirst:
- Reduce salt — salt drives thirst directly.
- Chilled water or ice chips in small amounts feel like more fluid.
- Sour sweets, chewing gum, brushing teeth can reduce thirst.
- Avoid swallowing mouthwash.
Signs of dehydration and overhydration
Under-hydrated (especially in heatwaves, vomiting, diarrhoea, long flights — these can cause acute kidney injury on top of CKD):
- Dark, concentrated urine
- Thirst, dry mouth
- Dizziness or lightheadedness on standing
- Headache, fatigue
- Less urine than usual
If you have CKD and develop any of these, especially with vomiting/diarrhoea, contact your GP or renal team — you may need to temporarily pause certain medications (ACE inhibitors, ARBs, diuretics, SGLT2 inhibitors — the 'sick day rules').
Over-hydrated (especially in advanced CKD, heart failure, dialysis):
- Swollen ankles or legs
- Puffy face in the morning
- Sudden weight gain (> 1 kg in 24 hours)
- Breathlessness, especially lying flat
- Cough, especially at night
- Rising blood pressure
These signs need urgent review by your renal team.
Best drinks for kidney health
If you're not on a fluid restriction, the kidney-friendliest hierarchy is:
- Plain water (tap is fine in the UK).
- Unsweetened tea or coffee (modest amounts — 2–4 cups/day; see our coffee guide).
- Herbal/fruit teas (avoid nettle and dandelion if on a potassium-restricted diet).
- Diluted squash (no added sugar).
- Skimmed/semi-skimmed milk in moderation (counts towards calcium and protein).
Limit: sugar-sweetened drinks (see our sugar guide), full-cream milk in large quantities (phosphate), and very high-sodium drinks like tomato juice.
