Guttering to run to 30,000l tank. Gutter should be covered to prevent debris. Cover needs to be removable (Perhaps clear for inspection purposes). MUST have sediment and leaf filtration in downspout, before entering tanks. <0.5 NTU does not require filtration before the tank. Sand filter then glass media filter. Take water from top of tank so sediment stays on the bottom. Downpipes – 125mm for 225m2 house, 12m maximum run. 2 x 125mm for 500m2 house.
How to build a sediment filter for spring water catchment: youtube.com/watch?v=tPkkoO6eXso
E1/AS1 is flawed as it uses 10 minutes of rain, allows a 1 in 50 flood, consider wind speeds specific to the building location, rainfall charts in E1/.AS1 are for 10-year return intervals. It also has no minimum fall for gutters, which in turn can affect water flow by over 100%. An increase in roof pitch also increases the roof catchment area and the volume and flow rate of water being drained. Use 200 mm/hour (2x usual).
100 mm diameter round downpipe will manage 210 m2 of roof (7850mm2). Use 150mm dia. pipe (for a single pipe for 500m2 roof)). A maximum spacing of 12 m is recommended.
Roughly speaking, 1 mm of rain over 1 square metre of roof equals 1 litre of water. This capacity can be calculated using the following formula: Annual rainfall (in mm) x Roof surface area (in square metres) = Roof catchment capacity. 750kL for 500m2 roof annually.
3x 25000l tanks to supply all properties, preferable bigger. 50mm/month average rainfall in summer = 25,000l in 1 month. Less 2,000l/day = About 12+ days to use. Based on one roof collection. BUT, 3 houses = 50,000l per month collected and 2000l/day used (60,000l per month) Therefore, 3 tanks are the minimum. Winter will catch 100,000l from 3 houses and use 60,000l.
In New Zealand, the average person uses 227 litres of water per day (140 in Auckland) :
- Toilet = 86 litres per day
- Bathing and hygiene = 68 litres per day
- Laundry = 36 litres per day
- Kitchen = 32 litres per day
- Housekeeping = 5 litres per day
rainharvesting.com.au/4-pillars-of-rain-harvesting-system-design/design-and-install-your-system
Climate maps: niwa.co.nz/climate/research-projects/national-and-regional-climate-maps