I've never heard of tap tds being that high. I'm in the Anglian Water region and we have some of the hardest water in UK, its usually around the 400 mark, did mine this morning and it's a little higher at 435. Even the waste water from my ro only  registers around the 500 to 600 mark, 800 is just nuts, definitely ring up  your supplier (presumably AW or could be Cambridge Water?) and have a chat.

Edit..and borrow a colleagues tds meter just to check yours isn't faulty.

Quote from: Splash and dash on February 24, 2026, 08:07:47 pm

Quote from: AuRavelling79 on February 24, 2026, 08:03:19 pm

Quote from: Andrew4444 on February 24, 2026, 07:20:23 pm

Thanks.  I will check.

I'm in st.ives but cambs one not cornwall.

Near huntingdon

I'm on the north west edge of Bristol and get supplied by Bristol Water. They use Chew Valley reservoirs in North Somerset AND draw off water from the Sharpness Canal in Gloucestershire which is fed by the River Severn.

I find after a lot of rain my tds DROPS. I've been window cleaning WFP from here since 2005 and the pattern is as follows -

After a lot of rainy days Input TDS250/300 output 4-6ppm. After a dry spell, Input TDS 350 plus output 7-9ppm.

I use an old Merlin type PRF R/O with the uprated membranes.

We used to do a bit of work in Bristol and the reading was 450-475

Wow! It is certainly higher because of all the limestone around Bristol. In general terms When you are getting water via the reservoirs from the Mendips it is higher. I don't recall mine ever going above 400. Never lower than 250 either.

Maybe because I am on the NW edge I get more of mine from Purton on the Severn/Sharpness side rather than the Southern side of Bristol? So mine is a bit lower overall?

My water pressure is good - normally between 60 and 65psi naturally so that helps the output.

Quote from: AuRavelling79 on February 24, 2026, 08:03:19 pm

Quote from: Andrew4444 on February 24, 2026, 07:20:23 pm

Thanks.  I will check.

I'm in st.ives but cambs one not cornwall.

Near huntingdon

I'm on the north west edge of Bristol and get supplied by Bristol Water. They use Chew Valley reservoirs in North Somerset AND draw off water from the Sharpness Canal in Gloucestershire which is fed by the River Severn.

I find after a lot of rain my tds DROPS. I've been window cleaning WFP from here since 2005 and the pattern is as follows -

After a lot of rainy days Input TDS250/300 output 4-6ppm. After a dry spell, Input TDS 350 plus output 7-9ppm.

I use an old Merlin type PRF R/O with the uprated membranes.

We used to do a bit of work in Bristol and the reading was 450-475

Thanks.  I will check.

I'm in st.ives but cambs one not cornwall.

Near huntingdon