dual supply gravity tank

kryan1

Has anyone plumbed a gravity water with 2 supplies, 1 supply is from a rain water harvesting system and the second is the mains supply.
I was thinking a float switch on d tank, and for it to be above the ballcock of the mains supply, so if it the rain water runs dry, it will then fill from the mains.
Anyone who has done this before, advice would be appreciated.

Many thanks

Kevin

nmacc

This is often done with two conventional ballcocks.

The rainwater supply feeds the first ballcock in the usual position. The second ballcock is mounted maybe 150 lower down. That way the tank is normally filled with rainwater, however if for some reason the rainwater doesn't refill the tank (such as no rainwater being available), then the mains will take over.

You might need to add a float switch if the rainwater pump is controlled by the pressure in the pipe. Otherwise it could run dry and damage the rainwater pump if you run out of rainwater.

PaulieC

Apologies for butting in (awful pun) on your thread, but my question was somewhat similar.

We did a big job on our hour a few years ago and part of it included moving the water tank from the attic to the shed (the water is pumped form there into the house). The location of the tank in relation to the roof would make it relatively easy to enable rainwater collection directly to that tank.

From some searches this morning, I cannot see if this is something that is possible (or advisable) to do. I can't think of any reason why not, but I have a few questions perhaps might be answerable here:

• How do you manage the two inputs in terms of favouring rainwater, but having mains backup ? From this thread it would appear that using two ballcocks is the answer.
• How much filtering is needed ? I'm not 100% sure, but I assume that the tank supplies water to everywhere except the kitchen sink and as such, would rainwater be suitable for showering, washing machine, teeth-brushing etc.

nmacc

In my case I'm running the washing machine, the outside taps & the toilets off the rainwater, teeth are washed and showers taken in mains water from a second cold water storage tank in the attic.

The amount of filtering depends on what you have in mind. Usually a coarse and a fine filter will do, provided you have a method of collection that keeps out leaves and also allows sediment to sink below the intake.

If you're going to use it for washing your teeth then you need a UV lamp to kill any nasties. Depending on the size of the dirt particles you may also need an extra-fine filter. For example I have seen problems with a system installed on a well-restored house; for several months the Blue Bangor slates gave off a fine black dust that went straight through the normal filters. It was harmless but unsightly, so a third filter was added to remove it.

PaulieC

I was hoping to avoid any major work as I do not believe that I will recoup the cost in the short to medium term, which means no new tank in the attic and all the plumbing that goes with it.
When we were doing the house a few years ago I brought up the underground tank option but it was vetoed by herself as being too expensive, when it really was the best time to do it. She now concedes that it was a good idea and should've been done. I mentioned this new plan last night to her and she looked at me like I had two heads, as if rainwater was poisonous. Personally I'd have no problem showering in filtered rainwater, or even brushing my teeth with it, but unless I get approval from the board, the plan is going nowhere.
I guess I'll wait for a year or so until the water charges really kick in and the demand for rainwater harvesting products and services go through the roof, taking the prices with them. Then it will be a good idea :rolleyes: