Size of backyard -> size of water tank

Hi,

I'm designing a new house with my builder and it looks like I will have a 250m2 backyard. It will be covered with grass and maybe a small garden. My gut feel is that I should get a water tank as otherwise I will spend fortune on water.

1. Am I right that I should get a water tank?
2. What size should I get to be able to maintain 250 m2 of grass?
3. Is there a high level formula that would give me amount of water a day/a week that I need to maintain 250m2 of grass?

I live in Brisbane.

Thanks

My gut feeling is that purely from an economy standpoint , it doesn't add up to install water tanks at this time, as water is still quite cheap (unless things have changed a lot recently). Note, this is just an uneducated guess by me.

But of course there's other benefits from installing tanks. The environment being at the top of that list. In times of drought it can minimise water usage, keeping dam levels higher. At very wet times it can prevent flash flooding & water pollution, when heavy rainfall on hard surfaces (roads, driveways & roofs) overloads stormwater & sewer systems.

You're also more likely to keep the lawn nice & green using free rain water (although you've already paid for the tank) than from mains water. Brisbane's rain is mostly over the summer months, so will keep the tanks topped up during those hot months your lawn will feel the heat.

Not sure about determining you water use in the garden. There is advice online though, for drippers & sprinklers. You can determine the flow rate of your sprinkler just by timing it to fill a bucket. Once you know how many litres a minute it uses you can determine it's usage, if you know how long it runs generally. But there's more to determining the size of your tanks than just your water usage. It's probably more important to determine how much water you'll receive. To do this you need to determine the catchment area (your roof area) & your average yearly rainfall. Lucky for you Brisbane has a nice high rainfall, about 1,200mm annually.

Plenty of online calculators for determining tank size, just google it. Here's one,
http://tankulator.ata.org.au

Here's a relevant forum post for you, though it's a few years old. Of course the economics changes if it's just water for the yard, or the toilets & laundry, or the whole house.
https://forums.whirlpool.net.au/archive/2018838

Also consider planting native plants where possible, which will require less water. Lawn is very thirsty.

Ps. I'm sure SaveH2O will come in with some much more educated advice soon

Thanks for the info. I will have a look.

I followed what was described here http://anewhouse.com.au/2012/02/what-si ... ou-need-1/ and assuming it is correct I doesn't make sense for me to install water tank. The most I can harvest is around 90kl (my roof does not seem to be as big as I thought . If I can use all of it, and I won't be able, I can save 90 * 3.5 = $315 a year. It will take me over 10 years to break even (for a 5k tank). And that does not even take into account pump running cost and maintenance costs. I think the answer to my question is No.

I wouldn't look at it on a ROI basis but you can pick up perfectly good second hand tanks quite cheaply. You also don't need a big pump if you use an 18mm garden hose from the pump to substantially reduce friction losses.

I would look at the 3 Ps to reduce the lawn's water needs by preparing the soil to retain moisture, deciding which grass is best suited to your needs, understanding the BOM national radar to see when rain is due, learn to recognise when the lawn needs watering by noticing when the grass is starting to wilt, watering deeply to encourage good root growth and supplementing light rainfall with additional watering if watering was needed prior to rainfall.

Use at least 15mm of water per sq m for a deep watering, this equates to 3,750 litres for 250 sq m. You won't get every drop out of a tank and as you can see, you will need a lot of storage capacity.

A problem with watering lawn is applying an even distribution with a sprinkler and you will need to recognise the disadvantaged areas.

It is also best to water early morning when the turf's water uptake is getting into stride and also to avoid evaporation losses.