Saturday, 3 May 2014

Rain water tanks - buy or build

An early decision as I plant the seeds that will eventually lead to a rain water harvest is whether to buy or build. Either way needs careful consideration of design features of the system.

Panasonic do a few rainwater tanks. They have a 150 litre tank for 55,000 yen, and a 200 litre tank for 70,000 yen. They also have a 340 litre wall tank for 65,000 yen. It actually looks like a wall, although I don't think any walls actually look like this. You'd have to get your house sidings redone to match it! Not sure if this was a translation error.

They are not the most expensive, but certainly not the cheapest. Maruichi have a 140 litre tank for 29,000 yen

There's a whole range of tanks here from Direct Tank, with and without lids. They look very simple, with a basic design, no frills, no included connecting parts. And expensive! For example a 300 litre tank with a lid for 52,000 yen.

Then there is Takiron, with a 120 litre tank for 29,700 yen. They also have a 150 litre wall type for 41,000 yen. You can pay more for something that is less attractive!

The best looking tanks may be either the German Groban Slimline 300 litre at 44,000 yen. Except that it's beige. Only 99 euros on ebay, so somebody is making a profit. It's got the ridges around the edge, which I'm not completely convinced about aesthetically, but I guess they have a pretty good functional rationale. 

Or the Aquatower, 150-200 litres depending where you put the tap for 39,700 yen. Or 100 litres depending which website you look at. They have a very clever looking drainpipe fitting which will stop dirty drizzle from getting into the tank, and also act as an overflow if it is aligned with the top of the tank. 

The best I can get is something like 150 yen per litre of storage. This is very close to the price I pay for each cubic metre. A cubic metre is 1,000 litres, so I would need to fill and empty the tank 1,000 times for it to pay off in purely financial terms. If I tried really hard I could probably fill and empty the tank 20 times in a year, so it would take 50 years to cover the initial cost

Of course everything is not purely financial. If I'd been interested in making money, I would probably have invested in shares of the oil industry or a nuclear power station rather than putting solar panels on my roof. Using the water off the roof will not only have benefits in reducing the demand for local water, and providing my garden with cleaner water than the tap does, it will provide a store of relatively clean water in the case of some natural disaster that destroys the municipal water supply. At least it would if such a disaster did not destroy my water system too. Anyway, I can probably build a system for much less than this cost, provided I spend several hours thinking about it, and not putting any financial value to that time.