20 or 25mm water meter on trickle feed supply

Getting ready to start on my home build, and have two options for water supply from the council, and was looking for guidance as to what I am better getting.

The area is trickle feed water, used to top up the rainwater tanks.
My block is a sloping block, with the house around 10-15m higher than the road level.
House is around 100m up the hill from the road.
I will be using 25mm piping from the output regardless of the meter.

The two options are

20mm standard domestic water connection $1414.41 and
25mm standard domestic water connection $1603.32

Don't mind too much the extra cost for connection, but the quaterly charge for the 25mm is 1.5625 times the 20mm.


The question I have for the plumbing type people is, taking in to account my location where it is trickle feed and my house level is around 10 - 15m above the road level is there any real benefit to pay the extra ?

Will the 25mm meter allow better flow when/if the water tank runs low enough to require topping up ? or am I just kidding myself, and would be better just sticking with the 20mm meter ?

I'm assuming its for domestic use and you use 1000Litres per day, that's going to be less than 1Litre/minute.

A 20mm should be plenty big enough.

So...there is a mains water supply but you will not be connected to it except to trickle top up the water tanks. Is this right? I have never heard of this before.

A trickle feed tank top up usually only tops up 100 mm of water once a pre set low level is reached. Have you worked out how much available water you will have left once that low level is reached? Given that you are on a slope, I assume that you will have multiple tanks rather than just one big tank.

Do you have the option of not having the trickle supply? The connection charges are high plus you also have to pay a quarterly fee. If you opt out, do you still have to pay a quarterly charge? You are in a high rainfall area, why not put the money into additional storage?


There would be negligible friction loss in both pipes with a trickle feed.

Makes a lot of sense to me. Going the larger 25mm won't make any difference whatsoever, well except for higher rates bill.

Just been spending hours going through your site... most interesting comments there.

Mains water, but not mains pressure. Means there's water to top up the tanks if we go below a certain level in them.

Just the one 32000 litre tank. Although considering additional tanks at a later date. We have lived on tank water for the last 28 years.



I only wish we did have the option.... well we do actually, but still have to pay the same if we don't connect.

If we could opt out and not be forced to pay for a (non-)connection, we would simply add more tanks, which is what we would prefer.




That's what I wanted to know... get the cheaper 20mm meter and pay the minimum quarterly payments.

Is it worthwhile to run 25mm pipe from the 20mm meter, or being on trickle feed stick with 20mm for the 100m up to the house, and just run 25mm from the water pump on the tank to the rest of the house ?

For the trickle flow 20mm pipe should be Ok.

Its worth going to a larger pipe (such as 25mm) for high flows such as feeding the house from the pump.

Sounds like a plan to me. Thanks for the quick reply.

Bummer!

I assume that the quarterly charge is fixed, that is, it doesn't vary as per the volume of water delivered.

Even a trickle of 1 lpm would give over 1,400 litres per day and one would assume that the trickle feed would be greater than this.

If you use Blue Stripe poly between the pump and the house, the internal diameter (ID) will be roughly 21 mm as this pipe is measured as an outside diameter (OD). A 21 mm ID pipe has a volume of .346 litres per metre. You can use this to determine the metres per second velocity at certain flow rates. This is a simple but effective way to determine the suitability of a pipe's size in relation to the pump.

Many people with larger pumps have undersized pipes. Class 12 pressure pipe has an ID of 29.5 mm while the class 9 ID is 30 .5 mm. PVC pressure pipe is easy to use, particularly when Clearpond Pondflex (black corrugated UV stabilised) tube is used for the flexible couplings. This is measured as ID. The 25 mm Pondflex has a pressure rating of about 680 kPa from memory.

Other factors obviously also come into play such as the run distance Vs friction loss consideration plus the tank's location given that the land is on a slope.

Re the pump, if it is submersible, have it raised off the floor or placed in a shallow container to prevent it from vacuuming the tank's floor.

If it is external, don't have the suction hose connecting to the pump via a 90 degree elbow fitted directly to the pump's suction side. I see this a fair bit and cavitation can be a b!tch.

Yep, fixed price every quarter, even if we did not connect up !




I sure hope so, and something I'm not sure everyone is fully aware of with trickle feed, is that over a day you can still get quite a bit of water back in to your tank, and that's even if the flow is really just 1lpm !



Still coming up to speed with the fact that piping is sold on a OD and not ID, so it's really a tad smaller that what you buy as such.



It is the friction losses and head of water that I was originally concerned with at the start, but now I have to consider the fact that the tank is mostly buried, with the tank top being below floor level of the house (~1m) and at its closest point to the house it is around 4 or 5 metres away.



That was how it was done in our old house, 2 x 90 degree elbows to get out of the tank, and a couple more under the ground to the pump !

Personally I'd prefer the pump to be outside of the tank for repairs and easy access, than in the tank itself. Point taken about keeping the suction point off the bottom so it won't suck up the inevitable silt build up.

Would you consider the idea of using larger than 25mm poly pipe, such as up to 40mm to go from the foot valve to the pump and from the pump to a point in the house, where it then gets distributed to the various outlets around the house ??

Note:
Not all pipe is measured on the outside. If the description was 20NB it would mean 20mm nominal bore.... (Gal pipe)