How does 添's 2021 meanings appertain to its semantic component 水?
添 is related to water because 添 is mostly referred to adding/refilling of liquid' e.g. 添酒，添水，添油 (add wine, add water, add oil)
酒 and 油 are not 水 but all characters related to liquid use 氵 as its radical, and 添 is too -- The most common and easy thing to add is liquid
添 = add --&gt; also --&gt;futhermore
Cantonese uses 添 as a modal particle expressing emphasis, which implies  'just remember/  be reminded'
Example:
唔記得買米 = forgot to buy rice
唔記得買米(添) = (oh/ouch/ just remember) forgot to buy rice
冇米點煮飯？ = how can dinner be cooked with no rice
冇米(添)！點煮飯？ = (oh/ouch/ just remember) there is no rice, how can dinner be cooked?
仲唔記得買米 = still/ also forgot to buy rice
仲唔記得買米(添)/ 仲(添)唔記得買米 = (furthermore), also forgot to buy rice

(Taishanese) need to (do something); have to

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