Rainwater Collection Workshop

See also:

Rainwater Harvesting - workshop notes

Part of Upper Hutt's Healthy Homes Happy Pockets programme

10am-12noon Saturday 19th February 2011
10am-12noon Saturday 5th March 2011
6-7pm Monday 7th March 2011 Stan Abbott at the Upper Hutt City Library

By Paul Kennett

Time table

  1. Intro Paul Kennett, Max Christenson and Dave Explain timetable for the morning and work done so far
  2. Outside to concrete in the 4th post with Quick-Crete
  3. Back inside to talk about rainwater tanks
  4. Break for morning tea
  5. Back outside to finish base and start work on connecting up bits
  6. Finish around 12noon. To be continued 5th March.

1. Intro

Paul Kennett - publisher and mountain bike track design and construction, DYI rain water tank 2007
Max Christenson - Pinehaven local hero, involved in the community hall and community garden
Dave - another Pinehaven local hero, with a lot of house and building design experience

Today we're going to spend some time talking about rainwater collection systems in general and the various options and gadgets and gizmos, then we'll have morning tea, then we'll go out and set up a 1000 litre tank outside for use by the Pinehaven Community Garden, right behind this hall. Then in 2 weeks time we'll connect the tank up to the roof guttering and connect it up to the beginnings of an irrigation system.

Then on the 7th March Stan Abbott will be giving a talk on rainwater collection; costs, benefits, regulations, types and design features - Stan is director of the Massey University Roof Water Research Centre in Wellington. He'll be providing a scientific perspective and probably focus on systems for producing drinking water. It'll be a good talk.

Last week some Pinehaven volunteers dug holes and concreted in 3 out of 4 poles for a base to put their tank on. Right now we're going to pop out and put in the last pole and concrete it in - then we'll come back and talk while the concrete sets.

Let's go out and have a look now.

2. Outside

This is the base we mostly built last week. We've left the last pole to sure what we're doing.

Main issues:

  • Location: under a downpipe and close to the garden, but also in this case out of view
  • I'll talk more about the tank we're using back inside
  • This base is designed for a 1000 litre tank which will weigh 1 tonne (1000 kg) when full (if you are building for a 200 litre tank it doesn't need to be quite this solid - but it will weight 200 kg's when full - so don't skimp, and do add strapping to the wall)
  • we're using 100x100mm fence posts (H4 treated timber) from any timber store, costing ???
  • cross braced with bits of wood we have laying around (100x50mm "2 by 4" would be fine)
  • The holes were dug 500-600mm deep
  • Holes were widened out (at least 300mm across) near the bottom so that the concrete will create a wide foot pad for the weight to spread over
  • First three holes were 2/3 filled with EasyCrete (just add water, sets overnight) we used 4 x 25 kg bags
  • We used a level to make sure each pole was vertical and measured it all to make sure we were
  • Add all the cross bracing to keep it all as strong as possible against side forces (eg Earthquake)
  • The last hole will be using QuickCrete (just add water, sets in 15 minutes)

3. Discussion


  • in the next water crises you'll be able to keep watering your garden
  • you could avoid putting expensively treated drinking water down your toilet
  • rain water collection helps to reduce the peak flow in a storm event
  • reduce your annual water bill (if water meters are installed)
  • reduce your burden on regional water systems
  • possible water source after disasters (earthquake, flood)

Issues with the 1000 litres tanks:

  • We're using a used 1000 litre tanks from Pacific Wallcoverings in Porirua, cost about $100 each ($85 in 2007)
  • Contained cellulose wallpaper paste (I've emailed the people who make it in the UK and they say it's also used in gardening as "Crystal rain")
  • Note! Pacific Wallcoverings also have tanks that contained out things (wallpaper glazing) which may not be as benign as the cellulose paste - you need to ask them for only the cellulose tanks (if you don't ask they'll sell you the closest one to hand)
  • Also more people ask for their tanks the price might go up
  • You need to clean out the tanks - I used a garden hose
  • Try to collect the goop - it will decompose over about a year
  • The tank walls are translucent - so you should paint or over them to avoid stuff growing in them. I put black plastic over mine. I've got some algae growing in them so I need to clean them out this summer.

Thoughts for 200 litre tanks

  • You could get away with a free standing base if you strap the tank to the wall

Main issues

  • Site assessment: What downpipes are available? Where could the tank(s) go? Where is the demand? [Note ground slopes up from Hall to Gardens]
  • How much water could you collect? How much do you need/want to collect? (Calculate an estimate of the amount of water your roof will collect.)
  • What space do you have for tanks (200l, 1000l or larger?)
  • Water used for; inside/outside - garden, toilet/clothes washing, bathing & drinking (potable)
  • DYI or professional?
  • Is your roof OK? (Lead paint, asphalt/bitumen, asbestos, treated timber/shingles)
  • Filtering (leaves, insects, bacteria) and ultra-violet lamp
  • Hutt Valley regional water catchment context
  • Why collect rainwater
  • Rainwater vs greywater vs blackwater
  • How much does your garden need?
  • How high can/should the tank be?

Household water use:

Bathroom 25%
Toilet 25%
Laundry 20%
Garden 20%
Kitchen 10%


Tips for saving water


  • Fix dripping taps. You can save up to 100 litres a day (that's up to 36,500 litres of water a year) just by replacing a worn washer - that's a saving of up to $54 a year!
  • Make sure your hot water system thermostat is not set too high. Adding cold water to cool very hot water is wasteful
  • Aerated taps are inexpensive and can reduce water flow by 50%.
  • Check for leaking pipes.
  • High water pressure increases flow rates from showers, taps, leaks and drips. If you have extreme high water pressure, a registered plumber can fit a pressure limiting valve at your property boundary.
  • A running tap can send 14 litres of water down the drain every minute.
  • High water pressure increases flow rates from showers, taps, leaks and drips. If you have extreme high water pressure, Council can fit a pressure limiting valve at your property boundary at no charge. Please contact us to arrange this. The owner needs to organise a plumber to recommend the pressure level required prior to the Council work being commenced.


  • For rinsing dishes or washing fruit and vegetables etc, half-fill your sink with water rather than leaving the tap running.
  • Use the minimum amount of dishwashing detergent (when washing dishes by hand) as this will reduce the amount of rinsing required.
  • Use a compost pile or worm farm for food scraps rather than a waste disposal unit. Garbage-disposal units use about 30 litres of water per day and send a lot of extra rubbish into the sewers. This places an additional load on sewerage treatment plants.
  • Use economy settings for small loads in your dishwasher.
  • If your Dishwasher does not have an economy setting, only do full loads
  • Each time you use a dishwasher you use on average 40 litres of water, or 14,000 litres a year.
  • When buying a new dishwasher, choose one that is water efficient.
  • For cold drinking water keep a container of chilled water in the fridge, rather than running the cold water tap until the water is cold.


  • Turn the tap off when you're brushing your teeth or shaving. If you brush your teeth twice a day, for two minutes each time, and leave the tap running, you waste approximately 56 litres per day - that's over 20,000 litres a year per person.
  • An average shower head with mains pressure uses at least 12 litres of water per minute. If you have an 8 minute shower that is 96 litres per day or 35,040 litres per year.
  • A water efficient/low flow shower head can reduce your water usage to between 5 and 7 litres per minute. They cost as little as $50 and can save up to 50 litres of water for each six minute shower, or up to 20,000 litres of water per person per year. An efficient shower will also reduce your power bill, as you use less hot water.
  • Showers use much less water than baths. The average bath uses over 150 litres. Only fill the tub with as much water as is required, for example you don't need so much when bathing children.
  • Take shorter showers - they also save you time and hot water costs.


  • The average single flush toilet uses 11 litres per full flush. A household with 3 occupants flushes, on average, 15 times per day which is 165 litres per day or over 60,000 litres per year
  • Modern dual flush toilets use only 3 or 6 litres of water per flush. This is 30% less than older dual flush cisterns and up to 8 litres less than single flush toilets.
  • A flush control device, such as a gizmo, will save significant amounts of water on most types of toilet cistern. It can save up to 30,000 litres per year.
  • If you can't install a gizmo a brick or zip-lock plastic bag filled with water can be placed in the cistern to reduce the amount of water used for each flush.
  • It is common for toilet cisterns to leak or overflow.
  • A leaking toilet wastes litres of water each day. Check for leaks by putting a few drops of food dye into the cistern. If you have a leak, coloured water will appear in the bowl before the toilet has been flushed. If you have a leak either adjust the water level in the cistern or you may have to get it repaired.
  • Check your toilet and hot water overflow pipes are not leaking.


  • 20% of your water is used in the Laundry
  • Ensure you have a full load of washing - each time you use your top loader machine you use 200 litres of water on average.
  • If you don't have a full load, adjust the water level or use economy settings to suit the size of your wash load.
  • Save water by reducing the rinse cycle.
  • When buying a new washing machine, choose one that is water efficient. Front loaders use about half the water that top loaders use. Look out for the 'AAA' Water Conservation Label - the more 'A's the more water efficient it is. Improved washing machines use between 45 & 165 litres per load and could save you up to $43 a year in water and power.
  • Save your 'grey water' from your washing machine rinse and use it to water the garden.


  • Water gardens in the early morning or late evening to minimise evaporation.
  • Try not to over-water - use a timer to remind you to turn off the sprinkler.
  • Don't leave hoses running. A running hose can waste up to 400 litres of water per hour.
  • Check for leaks on hoses and taps
  • Use mulch to minimize evaporation. Mulch helps the soil retain moisture, inhibits weed growth, and prevents erosion
  • Use a broom instead of the hose to clean paths and driveways
  • Over 80% of the water used in your home ends up as wastewater (sewage). If you reduce your water usage you produce less waste water. That means that less treated waste water is discharged into the environment.
  • Adjust sprinklers so they do not spray on paths, driveways and against buildings
  • When you clean your fish tank, use the 'old' nitrogen and phosphorous-rich water on your plants.
  • Water the garden early in the morning when the air is calm. Watering in the evening is the next best option. Heat and wind cause water to evaporate quickly.
  • Time watering your garden so you don't over water
  • Group plants with similar water requirements together so that you can tend to them without over-watering other plants. Remember, native plants require less watering.

Rainwater tanks

  • Install a rainwater tank or barrel. Using rainwater can reduce your water bills, as rainwater is free!
  • A rainwater tank can provide up to 65% of your household water usage.
  • Rainwater tanks reduce the load on stormwater systems, as roof runoff is not flushed into the drains.

How much water will my roof collect?

Annual rainfall (mm) x roof area (m2) x losses coefficient (assume 20% lost) - first flush diverter losses (litres x number of rain events) = water going in to your tank

Annual Rainfall from

  • Pinehaven Reservoir = 642 mm (2010)
  • Savage Park Upper Hutt = 842 mm (2010)
  • Akatarawa Cemetary = 1602 mm (10 year average 2000-2010). Ranges from 1131 mm in 2005 to 2197 mm in 2004.
  • Petone (Shandon Golf course) = 980 mm (10 year average 2000-2010). Ranges from 665 mm in 2005 to 1220 mm in 2010.

Pinehaven Hall

Pinehaven annual rainfall = 1000mm
13 m x 3 m = 39 m2
Losses coefficient 0.8
First flush diverter = 100 litre
Number of rain events = 50

(1000 x 39 x 0.8) - (100 x 50) = 31200 - 5000 = 26,200 litres

If there are downpipes at both ends, then assume half = 13,100 litres annually

Note: NIWA 5 year average per month

WELLINGTON Jan 72mm   Feb 62mm   Mar 92mm   Apr 100mm   May 117mm   Jun 147mm   Jul 136mm   Aug 123mm   Sep 100mm   Oct 115mm   Nov 99mm   Dec 86mm   TOTAL 1249mm

So December rainfall would produce

(86 x 39 x 0.8) - (100 x 4) = 2683 - 400 = 2283 litres (or 1141 litres if there are two down pipes)

Info sources

  • "Rainwater harvesting - beat the big dry", The Shed Makazine, April/May 2008, page 14-26:
  • "Rain Harvesting Systems safer solutions for rainwater collection", Marley (6 page brochure)
  • "Marley spouting and downpipe systems - your easy installation Guide, Rainwater solutions - ", Marley (10 page brochure)
  • "Rainwater on tap - save the rain for a dry day", 1 page instructions from mystery magazine, issue 45 1998, page 19
  • "Roof materials for rainwater collection", Massey University Roof Water Research Centre
  • "Greywater and your health - keeping healthy while using greywater in the garden", Kapiti District Council 7 page flyer
  • "Estimating the cost-benefit of rainwater tanks", by Stan Abbott,, 4 pages
  • "Rainwater Harvesting in Urban Environments - why not?", Stan Abbott, 15 pages "Currently more than 10% of NZers rely solely on roof water for their drinking water..."
  • EcoSac Storage,
  • Renew magazine


Page last modified on 19 April 2011 at 04:51 PM