Interactive lesson

Water budget, step by step

Interactive lesson: how much water you have and how much you need — house, garden, animals, spring, well and roof, then the critical month and a drought plan.

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The whole lesson as text

1. What a water budget is

A water budget is a simple sum: how much water comes in each month and how much goes out.

Two columns — On the left is supply: spring, well, rainwater, mains and delivered water. On the right is demand: house, garden, polytunnel, fruit and animals.
Each month separately — Springs and wells are highest in late winter and lowest from August to October. Demand runs the other way: it peaks from June to August.
The annual total misleads — A homestead with twice as much water as it needs over the year can still be 40 % short in August.
It needn't be perfect — A 20 % error is fine as long as you know which month is critical and roughly how much you are short. Your measurements improve every year.

Why: Most people only find out they are short in the second week of August, when the spring slows and the garden, the goats and the household all want water at the same time. By then it is too late for a tank, and the garden is already lost.

The critical month is almost always August or early September: measure then and plan for that month.
L/min × 1,440 = litres a day, because a day has 1,440 minutes.

2. How much the house uses

A house with mains water uses a lot, but only a small part of it has to be drinkable.

120 L per person — A house with mains water uses 100–150 litres per person a day (about 26–40 US gallons). The 4freelife personal plan uses 120 L.
Drinking and cooking — Drinking and cooking need 3–5 L per person. A family of four with 20 L of good water a day can get through any drought.
Shower, toilet, laundry — Shower 30–45 L, toilet flushing 25–35 L, laundry 15–20 L per person a day. Toilets and laundry don't need drinking water.
Measure your own house — Read the water meter two days apart and divide by the number of people and days. For July and August add roughly 20 %.

Why: A typical family uses 100–150 litres per person a day. Toilets and laundry take almost half, and rainwater or treated greywater is good enough for both.

If water from your spring or well has not been tested by a laboratory, don't count it as drinkable until it has.
If you have visitors for two weeks, count them as household members.