AFAIK and generally speaking, the hotter anything electrical/electronic runs, the shorter it's life. I'm guessing that if there's no fault the manufacturer is expecting you to be using more water which would dissipate the heat. If that's the case then maybe a circulation pump would cool the unit down a bit but that seems a bit of a faff for something that should be able to handle low/zero flow. See what the manufacturer has to say

Posted By: Cliff PopeI have fitted a UV treatment unit in the water pipe in the house, on advice following boring of our new borehole.

Begs the question as to why water treatment was deemed necessary on a (private domestic?) bore hole.
I have 3 bore holes, none have any water treatment and none have ever had quality problems.

IMO treatment is only needed if the water is contaminated to start with or contamination enters the system somewhere. If the water is contaminated to start I guess this is a bigger problem and I'm not sure that a UV unit will solve the problem and if contamination enters the system somewhere then this should be fixed rather than cleaning after the event.

2 of my systems are closed, that is from the bottom of the bore hole to the tap(s) there is nowhere for anything to get in and once the water is above ground it is pressurised so any leaks will push out rather than suck in. The 3rd system has a holding tank with an air vent so this is a possible source of contamination but in 29 years of operation there have never been any issues and periodic water checks have never shown any issues (and the health authorities have been happy with the installation when we have had public open days on the farm).

PS post construction treatment of each bore hole was to dump a good quantity of hypochlorite down the borehole, leave for 24 hours then pump out to get rid of any contamination from construction. After this no treatment has ever been done.

All good points - thanks.
The UV unit was cheap (£200) in the overall scheme of things - total about £13,000 for boring, digging trench, installation of pump, control unit, etc- and was advised as a precaution by the borehole contractors. They said in their experience testing for coliforms was meaningless because they could appear subsequent to the test anyway, so they strongly advised installing one anyway just in case.
I'm getting a general "safe to drink" test done in a few weeks to cover all the common contaminents, principally coliforms, iron and manganese as well as pH and hardness, after it has all had a chance to settle down.

The power of the lamp is determined by the flow rate when the pump is actually pumping, not of course the actual water consumption. Typically it cuts in about half a dozen times a day, hardly ever at night. It's a 55watt lamp, which I have confirmed by measurement. That's not much in heating terms, but confined in a very small space inside a highly polished steel tube it inevitably gets very hot, just like a light bulb if you confine it with too small a shade. So it's temperature is critically dependent on cooling by the water flow, which for long periods is nil.

I'm puzzled by how it can ever be expected to be satisfactory, or indeed safe from fire risk, given that the water only flows when the tank is intermitantly drawn and re-filled. I'll talk to the supplier and find out what they advise. It's very tempting to just wire it up to the pump so that the light comes on only when water is drawn.

Sounds like it wasn't properly designed or wasn't installed as designed. But that's just a top-of-my-ignorant-head reaction.

We had a UV lamp on our well at a previous place, a condition of our mortgage IIRC. We had the council come round and test for coliforms (pretty much guaranteed to be present at the low detection limit), they condemned the well, thus opening up grant funding which paid for the treatment system (pH, UV, filtration in our case in a kiosk outdoors). The previous owner had drunk the well water untreated for 70 odd years and looked very healthy, it was the best tasting tap water we ever had, no chlorine.

Iirc ours was 18W, the 55W ones are industrial size.

The UV lamp has a warm up time so it needs to stay on continuously otherwise a glug of coliforms would come through while it warms up and they would then colonise the house pipework.

The UV power is determined by the path length of water it has to shine through, is nothing to do with flow rate.

It's a fluorescent bulb so has a fixed operating voltage, you can't tweak the voltage based on flow rate.

If it got too hot, the water inside it would rise by convection up the pipes and lose heat through the pipe walls. It never got anywhere near to boiling temperature (100deg), and would subsequently have to boil the well dry before increasing to fire ignition temp (400+deg) so no chance of that.

There was ongoing cost for electricity and the bulbs, filters, pH media, need replacing every year so overall not as cheap as might be expected.

In county areas there will usually be a specialist water treatment firm who fit and maintain all the supplies locally, they will know about treating whatever minerals iron etc are present in the area.

Posted By: Cliff PopeI did once live on a farm with really polluted water, but the residents were never ill but visitors invariably were.

Absolutely, you get used to and tolerate with immunity your own bugs as found out by many holiday makers who arrive at their destination to get 'upset tummies' from the local water whereas the locals never have a problem.

Edit to add : LED system available now instead of fluorescent, looks promising

https://www.directwaterfilters.co.uk/private-water-supply/off-grid/12v-dc-uv-led-11lpm-ultra-violet-uv-water-treatment-systems.html

Cliff Pope
I don't get why you have 2 pumps. The bore hole pump will be a submersible pump which should be capable of pumping up to the loft tank. (if sized properly) How do you transfer from the bore hole pump to the surface (I presume) pump to fill the loft tank?

I was advisd that the borehole pump would have a shortened life if it kept switching on and off refilling the loft tank, and would need to be higher rated to pump down 100 metres of pipe from the borehole to the house as well as to the loft tank. Instead it comes on once per day to refill the much bigger holding tank, and also can then take advantage of the 1/3 price of economy 7 electricity.
There would also be a much longer insurance against running out of water because of power cuts or borehole pump failure.
The float valve in the attic would need upgrading and a much longer armoured cable all the way to the borehole.


The system uses the existing hardware - pump to take the water from well or rainwater tank to attic, piping all in place, so avoids having to dig up 50 yards of sloping rockeries and borders, negotiating existing uncharted network of pipes and cables, old and new, and crossing a stream. The tank was already there. The tank is next to a large shed which could easily accommodate any necessary filtration/treatment equipment if tests prove that necessary, with the bonus that it is frost-proof. Direct pipe to the house would need construction of another frost-proof shed close to the house.
This is probably all a bit unusual, but it keeps the whole thing simpler if the borehole simply supplies the holding tank, and the existing system supplies the house (and our nearby cottage) from thereon. It's also significantly cheaper.

The borehole is now fully commissioned and the whole set up works well. The uv was just meant to be an inexpensive precaution, probably unnecessary. Depending on what the UV supplier says, I'm tempted just to not bother using it.