The Etymology of “husband’s tea”

The concept of "husband's tea" may have originated as a description of tea that is not good enough "for company" (or for oneself) but adequate for the needs and indiscriminate tastes of one's spouse. An early instance appears in Lady Rosina Lytton Bulwer, The Budget of the Bubble Family (1840). The summary description of chapter 6 contains the following fragments:

Mr. Howard Makes a Resolution Which He Finds It Difficult to Keep, but Keeps It Nevertheless.—Birth-Day Presents.—Shopping.—Husband's Tea. The Reader Is Introduced to Mrs. Whabble.—...

The portion of the chapter to which the "Husband's Tea" snippet refers is this exchange in a confectioner's shop:

Mrs. Stafford, the confectioner, also sold Howqua's tea; and at the time Miss Prudence and her party entered the shop, a tall raw-boned Amazonian-looking woman, in an expensive but much soiled silk dress, an Indian shawl equally ill-used, and a flaunting scarlet-velvet bonnet, with a black feather in it, was making the following complaint, in a high-toned vulgar voice, to Mrs. Stafford.

"Oh, Mrs. Stafford! that last tea which you sent over to Gorget cottage, was so bad, that it was perfectly undrinkable."

"Indeed, ma'am! I'm very sorry, it must be a mistake—I'll change it with pleasure."

"Oh, no," said the first speaker, "its not worth while to do that, for it will do very well for the Major and the children, but let me have some better now."

Most other early instances emphasize not the inferior quality of "husband's tea" but its weakness, as if the term referred to a second pot of tea made with leaves already used once. This usage occurs twice in The Earthen Vessel: And Christian Record and Review (1850), cited in user240918's answer—first in "Snows' Fields Meeting on Behalf of the Christian Poor Society" (page 49):

Mr. [James] Wells illustrated the system of economy by referring to what he had done in his early days ; and went to declare that with fifteen shillings per week he had maintained his family, and saved sufficient to pay off some old debts. It may well be asked—"How could this be done?" Mr. W. shewed it was done by living principally on potatoes and bread, and a little "husband's tea ;" and that he was never stronger or better in his life than at that time. Now, if bread, potatoes, and a little tea, are the only things necessary to preserve a man's constitution, and to maintain his strength, we certainly think there might be less poverty than there is ; but we shall be the last to advise our hard working brethren in the ministry to adopt this mode of living, unless driven to it by absolute necessity : and too many of them, we know are often obliged to come on even shorter commons than this.

—and second (in what might be read as a response to the first instance) from "The Saviour's Solemn Caution Against the Sin of Covetousness Now So Prevalent in Our Professing Churches" (page 167):

What a wonderful change would the real lovers of God and truth behold in the state of the churches of Christ in this kingdom, if the ministers of the gospel, like Paul and Titus, led and encouraged the disciples by their example and practise, to remember the poor saints scattered over this land ; a good collection by a pastor of a large church, for some poor brethren at a distance, conveyed to the needy ones, by some truth-loving servant of God, would be more acceptable and scriptural, than a prescription for husband's tea and potatoes.

Likewise, "The Gambler," by M.A.B. in The Family Herald: A Domestic Magazine of Useful Information and Amusement, volume 10 (December 3, 1853) has this reference to "husband's tea" in the context of a visit by Mr. Warrener to the home of Charles and Agnes Morton:

"Is not Morton home yet?" he [Mr. Warrener] inquired; "I met him about six o'clock and he asked me to come in this evening."

"And he promised me he would be back by seven," said Agnes, still piqued at her husband's neglect, "so it shall be 'first come, first served.' There, take his easy chair, and don't let him have it all the evening. And I'll make the tea, and if he does not come soon he shall have husband's tea, which is only water bewitched, nearly cold, and no cream in it. At least that's what he will have if he gets his deserts."

And from a brief item originally printed in Mother's Friend, reprinted in The Christian Miscellany, and Family Visitor (November 1854):

"HUSBAND'S TEA."

"Well, I never! Mrs. Morris : why, how poor the tea has got all at once! Why, sure enough, it is as bad as 'husband's tea' now." This speech was made by a blunt, rough, rosy-faced matron, who was presiding at her tea-table, and entertaining a friend, who was a gentle, loving, and loveable young woman, that had not long worn a golden circlet, and been called "Mrs. Morris." "Thank you Mrs, Chubb: my tea is very good; and they say strong tea is not good for the nerves. But," continued Mrs. Morris, "what can be the meaning of 'husband's tea?' I have often heard the expression, and wondered what it could mean: do tell me."

"Why, as to the saying," replied Mrs. Chubb, "I am sure I don't know how it came among us; but I reckon that some wife, who liked her own dear self better than anybody else, used to drink all the strong tea, and leave water in the pot for her good man."

In a similar vein—but somewhat later—from Thomas Plowman, Acis & Galatea, or The Beau! the Belle!! and the Blacksmith!!! (1869):

Polyphemus. It's all up now with that conceited lubber [Acis]; / 'Twill do no good, so don't bewail and blubber. / But come and be my wife.

Galatea. Oh, wretched fate! / But you shall suffer for it let me state. / I'd die with Acis without more ado, / Could I not live to be reveng'd on you. / I'll promise you when I become your wife, / You'll find in me your greatest plague in life. / ... I'll hide your pipe, secrete too your latch key, / Water your beer, and give you husband's tea; ...

John Hotten, The Slang Dictionary: Etymological, Historical, and Anecdotal (1874), which both WS2 and user240918 allude to in their answers, includes this entry for "water-bewitched"

Water-bewitched, very weak tea, the third brew (or the first at some houses). Sometimes very weak tea is called "husband's tea," in allusion to the wife taking the first brew, and leaving the rest for her husband. Also grog much diluted.

The entry for "husband's tea" in Report and Transactions of the Devonshire Association for the Advancement of Science, Literature and Art, volume 9 (July 1877)—cited by the OED in the excerpt that WS2 includes in his answer—is included in "First Report of the Committee on Devonshire Verbalk Provincialisms" and reads as follows:

"HUSBAND'S TEA (= Weak Tea). A servant girl (2) calls Weak tea Husband's tea, and explains that whilst wives think such tea good enough for their husbands, they do not take it themselves. 19th March, 1877. W. P."

As Hotten's definition indicates, there is some inherent ambiguity regarding whether the weakness of "husband's tea" is owing to a lack of virtue in the leaves themselves, severe parsimoniousness in the doling out of fresh leaves for a potful, or a requirement that the leaves do double duty on a second ("husband's") pot. According to "The Word on the Waters," in The Quiver (1887), reuse is commonly the culprit:

Our sailors. however, have special temptations, and the Seamen's Mission tries to stem the tide of carelessness and irreligion. "We get hold of them," say our friends of the mission, "by all sorts of ruses, among which is a hearty tea."—"This is first-rate tea," said a grizzled old tar, with evident enjoyment ; "we get husband's tea at home—husband's tea, you know, is a little hot water poured on the grounds." The twinkle in his eye made his audience suspect that the best cup in the brew is usually "the master's," and that he was aware of it. After tea there is often hymn-singing.

But I suspect that different speakers may have had different causes in mind. And although Lady Lytton Bulwer's suggestion that "husband's tea" is simply tea of too low a grade to be served to important people may be the earliest recorded instance of the term, it may be that she misunderstood the sense of the term as used in common parlance because she couldn't imagine someone skimping on—or reusing—the essential ingredient.

The OED entry is instructive. Whilst it confirms the expression is obsolete (though I vaguely remember having heard it in my lifetime), I think the example given from 1877 comes as close as anything to explaining the etymology. The suggestion is that if a pot of tea turns out too weak, wives consider it fit only for their husband, not for it to be drunk by themselves.

husband's tea n. (also husbands' tea) Brit. colloq. Obsolete very weak tea. 1874 Hotten's Slang Dict. (rev. ed.) at Water-bewitched Sometimes very weak tea is called ‘husband's tea’. 1877 Rep. & Trans. Devonshire Assoc. Advancem. Sci., Lit. & Art 9 132 A servant girl..calls Weak tea Husband's tea, and explains that whilst wives think such tea good enough for their husbands, they do not take it themselves. 1895 Hampshire Tea 17 Aug. 6/4 Piled-up platefuls of cake and bread and butter and steaming cans of tea—not ‘husbands' tea’—were put on the tables.

According to Green's Dictionary of Slang it's a slang expression that probably compares a husband to a lover. The expression apparently was mentioned on a late 19th century edition of Hotten’s Slang Dictionary but its usage may well date earlier.

Husband’s tea (n.) [? a husband’s inadequacy as opposed to that of a lover] very weak tea.

• 1873 [UK] Sl. Dict.
• 1889–90 [UK] Barrère & Leland Dict. of Sl., Jargon and Cant.
• 1890–1904 [UK] Farmer & Henley Sl. and Its Analogues.

Also The following source refers to husband’s tea as weak tea, but doesn’t give details on its specific origin:

The earliest usage of "weak tea" as a pejorative beverage is 1825, in Robert Forby's Vocabulary of East Anglia, in reference to the word "lap," as in: to lap up your soup. Here, though, it's as a noun: lap being a diluted sustenance such as "thin broth or porridge; weak tea, &c." The same book applies the phrase to another, wilder one: "water bewitched," a colloquialism "used derisively for excessively diluted liquor; now chiefly, very weak tea." Years later, in an 1874 slang dictionary, "water bewitched" also had this note: "Sometimes very weak tea is called ‘husband's tea.’"

(Teasquared.com)

The following extract from The Earthen Vessel and Christian Record & Review dated 1850 appears to use husband’s tea with the above connotation:

Mr. W. shewed it was done living principally upon potatoes and bread, and a little “husband's tea;" and that he was never stronger or better in his life than at that time.