Rainfall
Reference location: Napier. 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 | 63.9 mm |
| Feb | 55.3 mm |
| Mar | 65.9 mm |
| Apr | 83.7 mm |
| May | 65.3 mm |
| Jun | 84.8 mm |
| Jul | 112.3 mm |
| Aug | 65.4 mm |
| Sep | 58.7 mm |
| Oct | 62 mm |
| Nov | 50.9 mm |
| Dec | 56.1 mm |
| Annual total | 824.3 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 25 days: NIWA’s average annual maximum consecutive dry-day length for Napier, 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 84% 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, Napier 1990–2019 annual rainfall extraction.
This roof and rainfall give an estimated annual harvest of 105,510 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.