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Kidneys and hydration

The kidneys that filter the blood, and the fluid and salt balance they manage.

Hydration is the everyday, trackable face of kidney and fluid balance. How much you drink, and how much salt you take in, both feed into it — and both are things a log can hold. For most healthy people the body's thirst does a good job, and the main practical target is drinking enough across the day, more when it is hot or you are active.

Kidney function itself is measured by blood tests — creatinine and the estimated filtration rate — and by blood pressure, since the kidneys and blood pressure are closely linked. None of that is visible on a tracker, but the behaviours that protect the kidneys, hydration and blood-pressure-friendly habits, are.

It is worth saying plainly that more water is not automatically better. The popular idea of drinking litres to "flush" the kidneys has little behind it for healthy people, and thirst is a reliable guide. The genuinely protective habits are keeping blood pressure in range and not overdoing salt — both of which sit closer to the heart page than to a water bottle.

Metrics that relate to kidneys and hydration

• Water intake
• Salt intake
• Kidney markers (creatinine, eGFR)
• Blood pressure

Calculators and reference pages that apply

Each of these is a real page on this site, chosen because it relates to this system:

The everyday levers

• Drinking enough across the day, more when hot or active.
• Keeping salt moderate.
• Managing blood pressure, which protects the kidneys.

What tracking can and cannot tell you

Tracking hydration is useful; measuring kidney function is a blood test. Do not force large volumes of water to "flush" the kidneys — thirst is a good guide for most healthy people.

Frequently asked questions

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