#45153 Laser (Pet peeve, again)

Fredjikrang · Post by **Fredjikrang** » Sat May 24, 2008 1:14 pm

Remember this?

Yeah. Looks like Yellow was in a hurry and didn't really read the question. *sigh* I will admit I spelled dechlorinated wrong though.

The end.

Wisteria · Post by **Wisteria** » Sat May 24, 2008 3:10 pm

I must admit, I am kind of confused about what you're trying to get at myself, Fred. But I very strongly doubt that there are bacteria floating around in the tapwater system. The water treatment plants do an incredible job of cleaning up the water, including several steps aimed at killing off microbial life forms.

Fredjikrang · Post by **Fredjikrang** » Sat May 24, 2008 3:39 pm

From my question:

The third was some tap water that had been declorinated (using sodium thiosulfate) and had been sitting in some big plastic barrels for a few days. This was by the far the best. The beam was more visible than with the algae, and it didn't seem to dissipate as quickly.

Aka, although it is true that there probably wasn't anything in the water when it was put in the tub, it had been sitting out at room temperature for a few days, uncovered, after having all remaining chlorine removed from the water. Still think it is so unlikely that there could be bacteria in it? We frequently have a couple kinds of life forms grow in these tubs, usually algae or diatoms are the only visible ones, but I am also pretty sure that bacteria live there as well.

I probably should have mentioned that fresh tap water didn't work as well, but I didn't think about it.

Yellow · Post by **Yellow** » Sat May 24, 2008 5:08 pm

Fair enough, I missed a a few details. But still, I don't think that dechlorination would take out all the other minerals, so that's my guess.

Wisteria · Post by **Wisteria** » Sat May 24, 2008 7:22 pm

Ah, I see. I agree with both Yellow and Fred now. Dechlorination will not remove the other chemicals, and leaving the tub out uncovered for a few days will probably spur some bacterial growth- but not much.

Fredjikrang · Post by **Fredjikrang** » Sat May 24, 2008 7:32 pm

I'm doing an experiment right now to try and clarify this a bit.

Look for some results in the next hour or two.

Fredjikrang · Post by **Fredjikrang** » Sat May 24, 2008 8:40 pm

Here is what I have come up with. This first image shows the laser beam in a variety of water from different sources.

I think you can see that the beam is a bit more visible in the old water than in any of the new water, but it is a bit hard to really tell, so here are two more images of the beams closer together in the water that we really are interested in.

This first one is water that has been in a tub for a while (a few days) vs water that has been in a tub for only a little while (a few hours.)

This second one has the old tub water compared to tap water both before and after being dechlorinated.

I think that it is pretty obvious that there is a substantial change going on here that can't be explained by minerals alone, though it does seem to also be obvious that the minerals in the water do account for about half of the effect.

What I really find interesting is that the tap water that has sat in the tub for an hour or so is clearer than the newer tap water (~10 min). Makes me wonder if there are really small bubbles that can't normally be seen by the eye alone but reflect/refract the laser light and so become visible.