Rainfall
Reference location: New Plymouth. 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 | 94.3 mm |
| Feb | 99.1 mm |
| Mar | 109.2 mm |
| Apr | 132.2 mm |
| May | 158.7 mm |
| Jun | 165.8 mm |
| Jul | 155 mm |
| Aug | 165.5 mm |
| Sep | 146.5 mm |
| Oct | 156.5 mm |
| Nov | 110.1 mm |
| Dec | 128.4 mm |
| Annual total | 1,621.3 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
- 60 m²
- Annual rainfall
- 1,621.3 mm
Assumptions for this example: a household of 4 people using 150 L per person per day (total 600 L/day), with a 60 m² roof. This is a stated example, not a recommendation for your home.
The reserve floor uses 18 days: NIWA’s average annual maximum consecutive dry-day length for New Plymouth, 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 81% 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, New Plymouth 1990–2019 annual rainfall extraction.
This roof and rainfall give an estimated annual harvest of 77,822 against an annual demand of 219,146. 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.