# Water Intake Calculator

> Estimates daily drinking-water needs from body weight (35 ml per kg) plus an allowance for exercise time, reported in litres, millilitres and 240 ml cups.

- Calculator id: `water-intake` · Category: Health (`health`) · Tool name: `calculate_daily_water_intake`
- Canonical page: https://tttkmbb.com/health/water-intake · This document: https://tttkmbb.com/health/water-intake.md · JSON definition: https://tttkmbb.com/health/water-intake.json

## Purpose

Estimates daily drinking-water needs from body weight (35 ml per kg) plus an allowance for exercise time, reported in litres, millilitres and 240 ml cups.

**Use when:** You want a practical daily fluid target for a healthy adult based on weight and activity.

**Do not use when:** The person has kidney, heart or liver disease, is pregnant, or works in extreme heat; medical advice supersedes this rule of thumb.

## Input

| Parameter | Type | Unit | Required | Description |
| --- | --- | --- | --- | --- |
| `weight_kg` | number | kg | required | Body weight in kilograms. (> 0, max 700) |
| `exercise_minutes_per_day` | number | min | optional, default 0 | Minutes of moderate exercise per day; adds about 355 ml (12 US fl oz) per 30 minutes. (min 0, max 600) |

## Output

| Field | Type | Unit | Description |
| --- | --- | --- | --- |
| `water_liters_per_day` | number | L/day | Suggested drinking water per day. |
| `water_ml_per_day` | number | ml/day | Same amount in millilitres. |
| `cups_per_day` | number | cups | Number of 240 ml (8 US fl oz) cups. |

## Formula

`water_ml = 35 × weight_kg + 355 × (exercise_minutes / 30)`

The 30–35 ml/kg rule is a common dietetic heuristic. EFSA's adequate intake for total water (including food) is about 2.5 L/day for men and 2.0 L/day for women; roughly 20–30% of that comes from food.

## Data Sources

- EFSA (2010) Scientific Opinion on Dietary Reference Values for water — https://www.efsa.europa.eu/en/efsajournal/pub/1459 (standard, retrieved 2026-09-23)
- Mayo Clinic – Water: How much should you drink every day? — https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/in-depth/water/art-20044256 (reference, retrieved 2026-09-23)

Data freshness: `static`. Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output.

## API

- `GET https://tttkmbb.com/api/v1/calculate/water-intake?weight_kg=…`
- `POST https://tttkmbb.com/api/v1/calculate/water-intake` with JSON body `{"inputs": {…}}`
- Response: unified envelope (`success`, `request`, `result.values`, `result.units`, `sources`, `freshness`, `timestamp`, `next_actions`, `links`); see https://tttkmbb.com/docs/response-format.md
- Schema: https://tttkmbb.com/api/v1/calculators/water-intake · OpenAPI operationId `calculate_daily_water_intake` in https://tttkmbb.com/openapi.json
- Authentication: none. Rate limit: fair use, see https://tttkmbb.com/docs/rate-limits.md.

## MCP

- Server: `https://tttkmbb.com/mcp` (Streamable HTTP, JSON-RPC 2.0, no auth)
- Tool:  `run_calculator` with `{"calculator_id": "water-intake", "inputs": {…}}`

## Example

- 70 kg, 30 min exercise: inputs `{"weight_kg":70,"exercise_minutes_per_day":30}` → `{"water_liters_per_day":2.81,"water_ml_per_day":2805,"cups_per_day":11.7}`
- 55 kg, no exercise: inputs `{"weight_kg":55}` → `{"water_liters_per_day":1.93}`

```
GET https://tttkmbb.com/api/v1/calculate/water-intake?weight_kg=70&exercise_minutes_per_day=30
```

## Limitations

The person has kidney, heart or liver disease, is pregnant, or works in extreme heat; medical advice supersedes this rule of thumb. The 30–35 ml/kg rule is a common dietetic heuristic. EFSA's adequate intake for total water (including food) is about 2.5 L/day for men and 2.0 L/day for women; roughly 20–30% of that comes from food. All values are computed from the formula above; no measurement or live data is involved.

## FAQ

**Does coffee or tea count?**

Yes, all beverages contribute to total water intake; caffeinated drinks in normal amounts are not net dehydrating.

**Can I drink too much?**

Yes. Drinking many litres in a short time can cause hyponatraemia. Spread intake over the day and drink to thirst during long exercise.

## Related

- [TDEE Calculator](https://tttkmbb.com/health/tdee.md) — Estimate calorie needs alongside hydration.