Why a range
The KX2 score is an estimate from a short check-in. Your body regulates fluid around set points,Source: Sex hormone effects on body fluid regulation, [6] and what’s enough shifts with heat and movement. A single perfect number would pretend to a precision that neither the body nor the measurement has. A range is honest about both.
No perfect score. No water-chugging competition. Just a range to stay in.
What the science says
No study has tested the KX2 target range. The research is clearest about too little; the upper edge is an open question.
- Small shifts can be felt.
- In young women, mild dehydration was linked to more fatigue and lower mood.Source: Mild dehydration affects mood in healthy young women, [1]
- Thirst isn’t the whole picture.
- Young women drinking about 1.5, 2.3 or 3.1 litres a day reported similar thirst.Source: Habitual total water intake and dimensions of mood in healthy young women, [2]
- Your baseline matters.
- In young adults, drinking more eased fatigue in low drinkers; cutting back lowered calm in high drinkers.Source: Effects of changes in water intake on mood of high and low drinkers, [3]
- Needs move.
- In young women, estrogen and progesterone shift how the body regulates thirst and fluid.Source: Sex hormone effects on body fluid regulation, [6]
What we don’t know yet
The edges of the KX2 target range, 50 and 80, mark where KX2’s guidance changes. Both are starting points, not yet validated.
- 50 to 80 is not a clinical range.
- The KX2 score is not yet validated.Source: Biomarker validation: testing the KX2 hydration measurement, [7]
- Each score is a snapshot from one check-in, not a continuous reading.
An open question: whether staying in the KX2 target range relates to how your days feel.Source: Does staying in the KX2 target range relate to better days?, [9]
What it means day to day
Check in when it suits your day. KX2 is designed to pair each score with one small next step.
- Below 50
- A glass of water mid-morning.
- 50–80
- Nothing to add. Keep your usual rhythm.
- Above 80
- Nothing extra needed for now.
Sources
Numbers match the Lab library.
- [1]Mild dehydration affects mood in healthy young women
Armstrong LE, Ganio MS, Casa DJ, et al. Journal of Nutrition, 2012
25 healthy young women (average age 23) in 8-hour laboratory trials, dehydrated by intermittent moderate exercise, in some trials with a diuretic.
Published science - [2]Habitual total water intake and dimensions of mood in healthy young women
Muñoz CX, Johnson EC, McKenzie AL, et al. Appetite, 2015
120 healthy young women (average age 20) grouped by 5-day food and fluid records into low, moderate and high total water intake (~1.5, ~2.3 and ~3.1 L/day, including water from food).
Published science - [3]Effects of changes in water intake on mood of high and low drinkers
Pross N, Demazières A, Girard N, et al. PLOS ONE, 2014
52 healthy adults aged 20–30 (41 women, 11 men): 30 habitual low drinkers (under 1.2 L/day) and 22 high drinkers (2–4 L/day, all women), studied in an inpatient unit.
Published science - [6]Sex hormone effects on body fluid regulation
Stachenfeld NS. Exercise and Sport Sciences Reviews, 2008
Review of research, mainly the author’s own laboratory studies, on estradiol, progesterone and fluid regulation in young, healthy women.
Published science - [7]Biomarker validation: testing the KX2 hydration measurement
Kronos Hydration Lab, 2026
No validation results yet.
KX2 validation - [9]Does staying in the KX2 target range relate to better days?
Kronos Hydration Lab, 2026
A question we want to answer, starting with women 35–50.
Active questions