Renovation : Gravity-fed versus Pressurised Water System ?

[DuraLexSedLex]

In the future we will need to renovate the gravity-fed system in our house.

Our plumber indicates that we have 2 options :
• The gravity-fed system is replaced with a new gravity-fed system or
• The gravity-fed system is replaced with a pressurised system.

The plumber highly recommends a replacement with a pressurised system.

But from my research, I understand that a pressurised system has drawbacks :
• The waste of cold and hot water is higher (higher flow rate).
• The risk of water shortages is higher (mains water shortages).
• The risk of pressure variations is higher (mains pressure variations).
• The risk of leaks and consequential damages is higher.
• The maintenance costs are higher.
• The installation costs are higher.

Why should the gravity-fed system be replaced with a pressurised system, given that our family has always been happy with gravity-fed systems ?

Note that our house has :
• Four occupants.
• A cold water tank in the attic.
• A hot water cylinder in the airing cupboard.
• Two showers with pumps and no bathtub.
• A flow rate of about 16 litres per minute at the tap in the garden.

That's an exceptionally biased post OP - I take it you are somebody that doesn't like change!

You have very good water pressure and showers, so pressurised will be far better for you. TBH I can't see why, given your helpful 'note our house' points, you would choose gravity again. From what you've told us is a no brainer.

For a large older property with low water pressure, then gravity would be a consideration but not necessarily the answer, but really not for you.
do more research without wearing your scared of change glasses!

If you run your house of mains pressure, you don’t need pumps or power showers. You get great pressure. It’s how American plumbing works and is more modern.

That said, if we slide backwards into more “third world” style water supply. As has been the case this summer in some areas, then you would be grateful for the water in your cold water holding tank.

Are you an optimist? Or a prepper?

We have a pressurised water system and the only drawback I can see is when the water goes off...well it goes off. No usage of water from the loft tank

We have rooms in our loft hence the builders installing a pressurised system

Oh I like the plus side of all of the cold water supply being direct from the mains, so the cold taps are potable

Weirdly I have two systems in my house pressurised and gravity. The only issue is when the water is off it’s all off for the pressurised system whereas I still have hot water from the gravity system.
its an odd house not a large one

I have replaced my gravity system a year ago with a new boiler and a Harlequin Heatstream.

It has all the advantages of a gravity system and a pressurised system without the disadvantages.

There are no tanks in the loft and I have hot water if the boiler breaks down and the Heatstream doesn't need to be serviced unlike a pressurised cylinder.

In some parts of the country it us normal to have all cold taps and outlets such as WC cisterns supplied at mains pressure, and only the hot water system supplied from the loft tank.

In other parts it is normal to have the bathroom cold taps supplied from the tank as well.

What is the mains flow rate, below which it is "normal" to have a gravity-fed system, for a house with 4 occupants and 2 showers ?

UK people generally seem to consider that one shower, running off a combi boiler that can deliver about 12litres per minute, is fine.

But not if you turn on a tap, or flush a WC at the same time and the flow drops.

So I suppose if you hope to run two showers at the same time you would need at least 24 litres per minute.

Which could be done with a cold tank and large cylinder, with shower pumps to make the pressure acceptable. This is OK if you are hearing-impaired..

But a better, late 20th century solution would be an unvented cylinder, and almost certainly a new, large water pipe right the way from the water main in the road. Old houses often have a half inch lead or iron pipe. A 25mm plastic pipe can give much better flow, and its flexibility means you are less likely to need elbows. You can probably fit 32mm if you want or it is a long run. Be sure to fit full-bore stopcock and service valves throughout. Houses with a combi boiler often have flow to bath taps deliberately restricted to prevent the hot water being too cold.

As any gardener will tell you, digging a trench is not a complicated job. If your old pipe is lead, you might even get a subsidy or free connection to replace it. Ask your water Co to test your drinking water for lead content before you do anything else. A competent local plumber should be familiar with conditions in your area, and maybe even in your road.