Water Audit - 2015

I'm in the process of preparing for a full day teaching session as part of a PDC run by David Arnold based in Violet Town. He's decided to focus on a permaculture principle for each of the sessions, and my focus is on Principle 4: Apply Self-regulation and Accept Feedback.

As part of this I'm running a workshop on a self-audit, so I decided to take a look at water, consumption and collection. I thought it important to also look at rainfall over the past year, to give a point of reference.

BOM recorded rainfall for 2015 at nearby Mangalore airport: 344mm
Our records show 297.5mm for our home - may not be entirely accurate. 
Mean annual rainfall for Seymour (1981-2010): 584mm.

Our household consumption was quite low compared to typical household - around 150-170lt per day for a family of 4. A big part of the reason is that we only use tank water - and it was a dry year. On top of that; we don't wash ourselves everyday, we use a composting toilet system and we are careful with use. When water is in abundance we tend to use more of it - in winter we will often have baths if the tanks are near full. If low we will have short showers less frequently.

I've been using more water in the garden during the warmer seasons than I have in the past, averaging 230lt per day. This is predominantly used from October till March, with little use outside of these months. I've noticed that it takes quite a while for the water to penetrate into the soil, and during the summer I'll spend about 1.5 hours watering most days. A good time to listen to my favourite podcast - The Permaculture Podcast with Scott Mann.

All in all we used considerable less than a typical household of the same size, which is surprising considering that we grow most of our own vegetable and fruit. See some facts and figures below...


Mains water used for irrigation 2015

Total land area not under cover or paved is about 350m2 (total land area is 584m2)

Jan - April: 35,000lt
May - August: 1,000lt
September - December: 47,000lt 
Total mains consumption in 2015: 83,000lt. Average of 227lt per day.

Household water consumption for 2015

Consumption from water tanks (no mains water used) has not been accurately measured. The main tank was about 1/3 full at the end of 2015, reserve tank was near full. If we assume a rainfall of 344mm, we had the potential to collect about 56,000lt of potable water and probably consumed about that in the household - maybe a bit more. I estimate between 150lt and 170lt per day for a family of 4.

Our total water consumption for a household of 4 was about 400lt per day. Melbourne average is around 550lt for 4 people (2011/12).


Potable Collection (drinking quality)

Total potable collection area: 163m2
Total potable storage volume: 31,000lt

Cellar corrugated iron water tank (approx 8,000lt)
Collection area from house = 66m2
Rain needed to fill from empty: 121mm
Overflow: To main tank
Main uses: Washing hands, drinking, watering nearby plants occasionally.

Main corrugated iron water tank (approx 23,000lt)
Collection area from house = 97m2
Rain needed to fill from empty: 237mm
Overflow: Storm water
Main uses: Household water use; kitchen, laundry, bathroom. Some nearby plant watering and water for chooks.

Non-potable Collection (livestock quality)

Non-potable tank collection area: 33.9m2 
Total non-potable storage volume: 1080lt

Bathtub collection (approx 250lt)
Area of shed: 4.3m x 3m = 12.9m2
Area of timber storage: 1.6m x 5m = 8m2
Total collection area: 20.9m2
Rain needed to fill from empty: 12mm
Overflow: Soil infiltration
Main uses: For filling watering can and watering nearby plants. Often compost teas / worm castings added.

Plastic drum collection (approx 190lt)
Bathroom / greenhouse = 13m2
Rain needed to fill from empty: 14.5mm
Overflow: Soil infiltration.
Main uses: Topping up pond in greenhouse, watering nearby plants and washing hands.

Greenhouse pond - storage only (approx 620lt)
No collection area
Area of pond = 1.53m2
Depth: 410mm
Overflow: Soil infiltration.
Main uses: Aquaponics and watering pot plants.

Non-potable Collection (contact with ground)

Main infiltration basin - front yard (approx 920lt)

Area: Approx 11.5m2
Depth before overflow: Average approx 80mm
Overflow: Stormwater
Main use: Soak into soil on path around garden beds. It takes about 10 hours to soak into the soil from when it's full.

Cellar (approx 835lt at 200mm, 2600lt at 600mm)
This was an unintended water catchment source, but has proved quite useful. Usually pumped out after the water has soaked into the infiltration basin.
Area: Approx 4.3m2
Depth: 200mm not unusual after 25mm of rain, up to 600mm which is quite high.
Overflow: Out of stairwell at 1400mm
Main use: Pumped to infiltration basin via laneway channel
Laneway channel, diverted to infiltration basin


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