water tank

Rainwater harvesting workshop

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I attended an interesting workshop this evening on rainwater harvesting, presented by John Caley, a sustainability consultant. This was organised as part of the Marrickville Council water tank rebate program.

A few notes from the evening:

  • It makes sense to connect as many uses as possible to the tank, because that will leave more space for the rain to fill back up (greater usage can be more effective than a bigger tank).
  • We get approximately 1,200mm of rain per year in East Sydney (3.3mm per day on average).
  • Multiply out the square metre area of your roof by the 3mm/day figure to get an approximate figure for litres per day. In an ideal world, the household consumption would fit within that.
  • Water usage from the hand basin and kitchen sink are not significant in the scheme of things.
  • The best strategy is to increase the area of the roof that water is collected from, rather than increasing the tank size. This gives a much greater benefit for the effort (and cost).

In general, the workshop highlighted the value of working out:

  • average amount of water that can be harvested per day from the roof
  • expected household usage of water
  • size of the tank to match

(Not that we did this, we just fit in the largest tank that was practical in the available space, and hoped for the best!)

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Water tank

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Water tank

One of the first jobs in the new house was to organise the installation of a rainwater tank. The main goal was ensuring that we could have the garden we wanted, watered when we wanted, regardless of drought conditions.

A water tank would also reduce our overall water usage, and plumbing into the washing machine and toilet was a possibility.

I received three quotes, one from a major business and two from local companies. Prices ranged greatly, and the big supplier was the costliest and provided the least (not a surprise).

What was a surprise was how few of the tank installers were prepared to work “off script”. They had a standard tank type (metal or plastic), standard tank sizes, and were uncomfortable with connecting to the plumbing.

Thankfully, the Marrickville-based supplier was great, asked heaps of to-the-point questions, and was comfortable with everything that we wanted to do.

The tank itself was cheap, only $1,600 for a 5,110L round Colourbond tank. We had it painted to match the colour of our roof (Manor Red). Having space beside the house was a huge advantage here, as it allowed us to install a round tank rather than the ‘narrowline’ (and more expensive) tanks.

We were also able to get away with a bed of “crusher dust” instead of a concrete slab, due to the flat space beside the house. (This saved us at least $1,000.)

Doing a proper job, however, the costs added up, including:

  • Hookup to two downpipes with first flush and leafeaters = $800
  • In-tank sump pump (powerful model for front and back gardens) = $800
  • Connection to toilet and washing machine = $600
  • Filters = $300

All up, the cost was $6,200 including GST. Not cheap!

Thankfully there are plenty of rebates on offer at the moment, and we’re expecting to receive the following:

So that’s a net cost of $3,400 after all the rebates.

It’s a great tank, and the installer did a wonderful job. It’s big enough to serve our needs well, and the recent heavy rains are rapidly filling the tank up.

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