Help needed with data preparation (using M)

Hey ppl!

I've received a new task and need to learn M fast.

Problem is, I have a "simple" problem to solve but didn't learn enough M yet to solve it in a timely manner.

Hope you guys can help.

I have a table called "Update" with a single column "When" and single row containing one date.

Like this:

TABLE Update
When
28/02/2020

This date is dynamic, obtained by a query.

I have a second table "Water_Consumption" with a date column "Reading" and a column named "m3" formatted as number (integer). Like this:

TABLE Water_Consumption
Reading                m3
22/12/2019          210
22/01/2020          208
22/02/2020             0
22/03/2020             0
22/04/2020             0

My problem:
I need to change 0 to null when the date is greater than the date in "When".

So in the current example, my Water_Consumption table would look like:

TABLE Water_Consumption
Reading          m3
22/12/2019     210
22/01/2020     208
22/02/2020        0
22/03/2020     null
22/04/2020     null

This is as far as I could go, it works but requires me a manual update every month:

Table.ReplaceValue(#"Previous_step", each [m3], each if [Reading] <= #date(2020, 2,28) then [m3] else null, Replacer.ReplaceValue, {"m3"} )

Problem is, I need to make it update automatically so my current "solution" doesn't cut it.

Can you guys please advise?

Thanks in advance!