Building Construction, Renovation, Maintenance & Advice

Low Water Pressure

"Waiting For Godot"
"The case of the dribbling tap"

It dribbled.

It was a boringly slow dribble.

What had started as a glorious energetic morning had, once again, been reduced to lethargy. It was like this every morning. He'd jump out of bed eager to get into another productive day only to find that turning on the shower, rather like the relaxed but somewhat stubborn 'wait awhile bush' (Aussies know what I am talking about), suddenly grabbed his attention with the clear inescapable message “just hold on a minute, you are under my power and like it or not you're going to have to wait a while.”

The water dribbled pathetically from the shower head, he could almost hear it mumbling “oh no, you don't want another shower do you? You only had one last night. I can't be bothered.”

While the pressure, or lack of it, was bad enough, waiting for the hot water was even worse. He should have realised when he first took on this house and came across the skeleton sitting covered in cobwebs on the bathroom stool still with a towel wrapped around its waist.

He had named the shower Godot and, like Beckett's characters, he had become very creative at passing the time as he waited. He soon got bored counting the tiles on the floor. Playing nerdy games on his iphone kept him occupied for a week or two. He tried crosswords but it's hard to concentrate when your feeling like you want to strangle someone. Then he got serious and had a pretty extensive library installed in the bathroom seeking out 500 page doorstops novels to pass the time but then, still without hot water, he started contemplating self mutilation and suicide.

Enough was enough so in desperation he called the emergency number of the Bali Association of Professional Plumbers, they only have 2 members but they do provide a very helpful counselling service for people suffering from PAS (plumbing anxiety syndrome). They were very supportive and gave him some useful information regarding the most painless ways of moving oneself to another spiritual realm.

So what was it that had lead to this debacle, where was the ever absent Godot? In fact a combination of factors had contributed to a water system that simply didn't work.

The first factor was that the bathroom was up on the fourth floor of a very tall house, indeed oxygen cylinders were supplied at the bottom of the stairs for anyone contemplating an ascent. The water pump was powerful enough but, set at 30 to 40 psi didn't give much pressure at the showerhead 22 metres above.

Measurement of water pressure

Let us first get to grips with the figures. psi (pounds per square inch) are those old imperial units that should have died with the ark but are of a very convenient size when talking about water and air pressure and this could well be why they are often still used on tyre pressure and water pump gauges.

There are, of course, other units of measurement for pressure, for example divers (or anyone else with water in their ears) use the 'atmosphere' which is the pressure of the air at sea level and is equal to 14.7 psi. For you who think in the more progressive metric headspace 1 psi equals 6.89 kilopascals (kpa) and a bar (almost the same as an atmosphere) is 100 kilopascals or 14.5 psi.

All very interesting if you are mathematically inclined, pretty boring if you aren't but don't worry about it. Have a nice cup of tea and a chocolate biscuit and let's see how this applies in practice.

The effect of height on water pressure

Water is rather heavy stuff. If a diver goes down 10 metres the weight of water pressing down on him increases the pressure by an atmosphere (an additional 14.7 pounds of weight on each square inch of his skin) on top of the air pressure at sea level. The same applies to water pumps, you will need to pump water up to a pressure of 14.7 psi to lift it 10 metres.

In our problem house with a shower head 22 metres above the surface of the water in the water tank the pump will have to pump a pressure of 32 psi to get it up there. This pressure will only just get the water up there, it won't give you any additional pressure to make a dribble into a squirt (it is a little known fact that pressure is needed to turn dribbles into a squirts).

In the house with our Godot problem the water pump was set between 30 and 40 psi. Pumps of this type have 2 switches, the first senses when the water pressure is low and switches the pump on (in this case 30 psi) and the second when the pressure is high which switches the pump off (40 psi). It can be seen that the pressure in this system would have varied between 30 and 40 psi and most of this pressure was needed just to lift the water – no wonder it just dribbled.

Large Diameter pipes and a long wait for hot water

This house had a second problem in that someone had either wanted to sell more “stuff” or simply had that fateful tendency that non engineering types have of making things bigger “just to make sure”, in the absence of knowledge the word “overkill” tends to spring to mind. The pipes in this house were a dog's breakfast of expensive green pipes. Because the position of the pump had not been thought about carefully an additional 17 metres of pipe had been used. To add to the problem even further the inside diameter of the pipe was a somewhat obese 20 mms (millimetres) when 12 mms would have been adequate.

As a result of 17 plus 22 metres of 20 mm diameter pipe the pipes had 12 litres of cold water in them which would have to be replaced by hot water before the hot stuff reached the shower. 12 litres at a flow rate of one nat's bladder per second - no wonder Godot never arrived. By using a more sensible 22 metres of 12 mm diameter pipe only 2.5 litres of cold water would need to be replaced by hot which would bring the hot water delivery time down from around 20 years to a mere 2 days.

To add yet more support for Godot's recalcitrant cause someone with a wicked sense of humour had decided that a 50 litre hot water tank was large enough so by the time the hot water did get there (if it ever did) the tank was already minus a quarter of it's hot water.

Steps to reduce your water pressure problems

So, to make sense of all this:

If you have low water pressure check the pump pressure and the height difference between the surface of the water in your water tank and the height of the showerhead or other water outlet. For every 10 metres of height difference you will need about 15 psi of water pressure and then a further 15 or 20 psi to give a good healthy pressure in the water flow. You can get someone to adjust the pump to give you this.

To get hot water quickly you need good pressure and small diameter hot water pipe (12 mm internal diameter is alright). You also need a reasonably short pipe length directly from the heater to the shower. Bear in mind that in Bali where the ambient temperature is always quite warm you won't need oodles (an oodle is an alpine measurement of volume and comes from the Swiss word 'oodle' meaning cow's udder which was popularised in the lyrics of yodelling songs sung by frolicking milk maids who have a bit of a thing for bovine breasts) of boiling hot water for your shower so a small diameter pipe will suffice.

Finally a rule of thumb for storage water heaters – you will need a 50 litre tank for a kitchen, an 80 litre tank for a bathroom and a 100 litre tank for 2 bathrooms. Solar water heaters need larger tanks.

As for Godot, I wouldn't bother waiting if I were you.

Copyright © Phil Wilson 2011
This article or any part of it cannot be copied or reproduced without permission from the copyright owner.

9 December 2017 Copyright © Mr Fixit,
Jl Bypass Ngurah Rai, Gg Penyu No 1, Sanur, Bali 80228, Indonesia
Telephone: +62-361-288-789, Fax:+62-361-284-180