Rainfall
Reference location: Christchurch. Monthly rainfall is shown in millimetres; the annual total is the sum of the twelve months. This point profile is a planning reference, not a representation of every microclimate across the region.
View exact rainfall values
| Month | Rainfall |
|---|---|
| Jan | 45.3 mm |
| Feb | 39.1 mm |
| Mar | 48.5 mm |
| Apr | 62.5 mm |
| May | 65.1 mm |
| Jun | 71.6 mm |
| Jul | 64.6 mm |
| Aug | 67.6 mm |
| Sep | 43.8 mm |
| Oct | 50.1 mm |
| Nov | 43.3 mm |
| Dec | 50 mm |
| Annual total | 651.5 mm |
Source: Manaaki Whenua – Landcare Research, Data for A History of Open Temperature and Rainfall with Uncertainty in New Zealand (HOTRUNZ), version 1.0 (retrieved 2026-09-15).
Worked example
- Household
- 4 people
- Roof catchment
- 160 m²
- Daily demand
- 600 L/day
Assumptions for this example: a household of 4 people using 150 L per person per day (total 600 L/day), with a 160 m² roof. This is a stated example, not a recommendation for your home.
The reserve floor uses 26 days: NIWA’s average annual maximum consecutive dry-day length for Christchurch, where a dry day has less than 1 mm of rain. It is a climate normal, not a worst-case limit. Source: NIWA, The Climate and Weather of New Zealand, Science and Technology Series Number 74.
The lower-rainfall check scales each monthly normal to 72.3% so its annual total matches the 10th percentile in the extracted 1990–2019 series. This is a sensitivity scenario, not the monthly pattern of a particular year. Source: Manaaki Whenua – Landcare Research, HOTRUNZ version 1.0, Christchurch 1990–2019 annual rainfall extraction.
This roof and rainfall give an estimated annual harvest of 83,392 L against an annual demand of 219,146 L. Tank capacity does not change the amount of rain collected or the household's demand.
See our 25,000 litre water tank for details on a tank in this size range.