Water Levels (Tools)

[Stewpot]

In anticipation of me soon completing on the plot I'm buying, I've just bought an old fashioned water level. I did think about a laser level, but it seems to me that they just have too many limitations to be of much use. And the affordable ones have questionable accuracy (apparently).

 

Now, I think I understand the water level pretty well - it's dead simple; water always finds it's own level, so two ends of a tube filled with water, even if they are separated by a distance will show the same level. But, in fact, in its simplicity, it is deceptive. There are a great many videos on Youtube that show how to use a water level. Nearly all of them are wrong. Some of them, at best, don't really demonstrate the tool to its best ability, but most of the ones I've seen simply don't understand the principle they're demonstrating.

 

Here is one of many typical examples - can you figure out why he's wrong?

 

www.youtube.com/watch?v=8NdKsIp1KdU

[Hobbiniho]

hmm i am trying to remember back to my doing my HNC and the site surveying module i am pretty sure that it has to do with the amount (length and elevation) of hose is only good to level between two points if any of the points move you need to establish a new "level" so can only do 1 "leg" at a time 

 

depending on what you are planning on doing yourself on the build you could invest in a dumpy level you can get a cheap one for about £150 plenty accurate enough for most things as long as you set up a few good solid benchmarks

[nod]

I used water levels on a daily basis for setting out ceiling perimeter and a string line for the hangers Apart from being slow It’s now outdated 

It’s true that most of the cheap lasers are not that accurate and of no use for setting out foundations 

You can hire a really green laser kit on a daily basis for not a lot of money That you can set your foundations out in a day and if you set internal datums when the structure is up Floor screeds door heads etc can all be measured off these 

[Vijay]

Not sure I agree that the cheap rotary levels are not accurate. I bought one off Ebay and tested it against a water level over 30+ meteres - it was spot on. I've had no regrets buying one, although it probably wouldn't last on a true building site

[JFDIY]

I'll really depends on how much work you're going to be doing yourself.

I see no limitations to a laser level and I'd say that once you have one you will use it a lot more than you expected

 

If you're going to do the setting out in any way then I'd buy I used proper laser level and receiver, spend £300 on say a Leica Rugby unit and a receiver that reads in mm (such as a rod eye 160) and you can work solo in the bright daylight etc. The lower spec receivers only tell you when on-grade and make the job a bit slower that's all

 

When you're done with it you will get your money back selling it on.

 

Best money I spent, especially when doing brickwork and setting out. I even put my guttering up using it.

[jfb]

5 hours ago, Stewpot said:

Here is one of many typical examples - can you figure out why he's wrong?

i can't say I managed to watch the whole video but I am struggling to see what is going to lead him to have an wonky pool!

[JFDIY]

5 hours ago, Stewpot said:

Here is one of many typical examples - can you figure out why he's wrong?

He's not accounting for the change in capacity of the tube as he moves around, if he had a mark on the tube and moved the tube up or doen to meet the mark each time then he would achieve level, otherwise he's just getting random levels, might only be a few mm difference though as he's got a large reservoir of fluid on one end which will damp the effects a bit.

[Stewpot]

24 minutes ago, JFDIY said:

He's not accounting for the change in capacity of the tube as he moves around, if he had a mark on the tube and moved the tube up or doen to meet the mark each time then he would achieve level, otherwise he's just getting random levels, might only be a few mm difference though as he's got a large reservoir of fluid on one end which will damp the effects a bit.

 

...wins the prize

 

45 minutes ago, jfb said:

i can't say I managed to watch the whole video but I am struggling to see what is going to lead him to have an wonky pool!

 

Consider this: he starts off next to his base station bucket, and the level on his measuring staff reads (let's say) 20". Now he goes away from the base station, and the measuring staff reads 30". He tells us that he is now 10" lower than he was, but he is wrong. This is because he has filled 10" more tubing with water, and the only place that water can have come from is the bucket, which means that the level in the bucket is lower than it was when he started. Because the level at the measuring staff is the same as the level in the bucket, that is also lower than when he started So he must be more than 10" lower.

 

Now he takes his measuring staff to another point and finds that it reads 15". He tells us that he is therefore 5" higher than the base station, but he is wrong. This is because there is 5" less  tube filled with water, and the only place that water has to go to is into the bucket, so the level in the bucket is higher than it was when he started. The level at the measuring staff is therefore higher as well, so he is less than 5" higher.

 

If he was using a conventional, two-ended tube, with one end fixed in place at the starting point, instead of his base station bucket, the error would be more obvious - if you raise one end of the tube, the water will drain out of that end and into the other. The water stays at the same level relative to itself, but not relative to the starting point.

 

His mistake is to have fixed the tube to the measuring pole. This is how he should do it to get accurate results:

 

Start off at the base station, with the tube held against the measuring staff. With a marker pen, mark the water level on the tube. Now, he takes the tube and the measuring staff somewhere else, and holds the tube against the staff again. But now he adjusts the tube up or down until the water level is at the mark. At this point the water level is at the same place as it was when he started. Now he can read the level off against the measuring staff, and will have an accurate measure of how much higher or lower he is.

 

The important thing is, you must align the water level with the mark on the tube before you can gauge any meaningful change in the height of the staff. A ready made water level will have calibrated ends, to save you the trouble of marking it - you just note the number on the calibration. The beauty of this is that you don't have to see both ends of the tube - if one end is at the calibration mark, the other must be as well. That means you can be out of sight of the other end of the tube, perhaps round a corner, or the other side of a wall - as long as the water is at that calibration mark, you can measure a change in height with it.

 

Alternatively, if you were to use a measuring staff at both ends, with the level fixed to them both, you could simply measure the difference in height between them, without needing to use a calibration mark, but you would need to be able to take the readings at both ends at the same time, which probably requires a second person.

 

You can use a water level indoors, outdoor, round corners, over walls, in bright sunlight, it will never become inaccurate, never need recharging or new batteries, doesn't need a receiver, and only costs eight quid.

[jfb]

yes that all makes sense - i've only used a simple tube without a bucket so this isn't an issue.

[JFDIY]

14 minutes ago, Stewpot said:

You can use a water level indoors, outdoor, round corners, over walls, in bright sunlight, it will never become inaccurate, never need recharging or new batteries, doesn't need a receiver, and only costs eight quid.

 

Agreed, you can, but I'd still prefer to use a laser, because I can use it on a frosty day. I can also be set up and running within a couple of minutes and referenced to the site datum, and if I lay the measuring equipment down the water doesn't escape.

 

I'm all for saving money (often more-so than most) but i'd still buy a decent laser and receiver.

 

 

[Cpd]

For work I used to use water levels, inclinometers, and string lines and then I got two good quality laser levels, a rotary one for big set outs and a pendulum one for close work. I have never looked back and even now after I have given up my trade I still use them often on the building site, garden layout and drainage. I would never go back to the dark side. 

[Oz07]

Surely if you had a massive hose with no bucket you would always get same level? Mark a line on first leg take hose to other. Make sure water line level with first mark then mark second leg. 

[Ed Davies]

2 hours ago, Stewpot said:

Consider this: he starts off next to his base station bucket, and the level on his measuring staff reads (let's say) 20". Now he goes away from the base station, and the measuring staff reads 30". He tells us that he is now 10" lower than he was, but he is wrong. This is because he has filled 10" more tubing with water, and the only place that water can have come from is the bucket, which means that the level in the bucket is lower than it was when he started. Because the level at the measuring staff is the same as the level in the bucket, that is also lower than when he started So he must be more than 10" lower.

 

Indeed, but not much. Suppose his bucket is 200mm across and his pipe is 8mm ID then the proportional change will be R²/r² = 100**2/4**2 = 625. I.e., his measuring staff would have to be 625mm off its initial position to get 1mm of error. If the initial position was in the middle of the stick it wouldn't be long enough to get that much error. 1mm is probably about the level of accuracy you can read the water level anyway.

 

Still, the moral of this tale is to use a wide bucket rather than a tall one. Most of the water in his container is contributing nothing to the proceedings.

[Stewpot]

3 hours ago, Oz07 said:

Surely if you had a massive hose with no bucket you would always get same level? Mark a line on first leg take hose to other. Make sure water line level with first mark then mark second leg. 

 

The size of the hose is not a factor, and the fact that he's using a bucket as a 'base station' is somewhat distracting. It's his understanding of how the water level works that is wrong. He (and he's far from alone in this, if the videos on Youtube are anything to go by) is of the opinion that the level of water will always be at the same height, regardless of what relative positions the ends of the tube are at. This would be much more marked if both ends of the tube were the same diameter. So, yes, you are right - you have to mark the tube itself with the initial level, and thereafter, you always have to align the water level with that mark to get a meaningful reading.

 

[Stewpot]

3 hours ago, Ed Davies said:

 

Indeed, but not much. Suppose his bucket is 200mm across and his pipe is 8mm ID then the proportional change will be R²/r² = 100**2/4**2 = 625. I.e., his measuring staff would have to be 625mm off its initial position to get 1mm of error. If the initial position was in the middle of the stick it wouldn't be long enough to get that much error. 1mm is probably about the level of accuracy you can read the water level anyway.

 

Still, the moral of this tale is to use a wide bucket rather than a tall one. Most of the water in his container is contributing nothing to the proceedings.

 

Your point is quite correct (and shame on me for not having done that maths), but his use of a bucket is simply disguising his misunderstanding of how to use a water level. Most water levels just consist of a tube (often with a graduated vile at each end), and the mistake he makes would result in a 50% error.

[Simplysimon]

they work perfectly as long as there are no bubbles in the tube.

[Tennentslager]

Used one once with blue food dye in the water...built 13 pillars and when the 4.8 m joists arrived it was time to see if it worked.

100% accurate? but until I discovered Makita LXT I was a troglodyte or should that be Luddite

[SteamyTea]

Say you have 10 points to mark out, then ten tubes.

All ten tubes are tied together at your datum point, then the other end of each tube is were you want your level.

 

Probably cheaper to by a cheap laser level.

[Ed Davies]

59 minutes ago, SteamyTea said:

Say you have 10 points to mark out, then ten tubes.

 

Why can't you just move the tube?

[SteamyTea]

46 minutes ago, Ed Davies said:

Why can't you just move the tube

Well you can, but I thought this was about making an easy job difficult and messy,