The Water Cure author Sophie Mackintosh on sisterhood: 'It is one of the most intense forms of love'

My relationship with my younger sister has gone through many phases: from being so close as children that we had our own language, to the usual teenage quarrels, to today, as I prepare to be the maid of honour at her wedding. I can’t quite believe that we’ve been partners in crime for almost three decades already. Being a sister has always been such a crucial part of my life, so it felt inevitable that my debut novel would focus on this relationship: complex, often fraught, yet hopefully underpinned with a great tenderness. Nobody can love you more, and yet despite (and because) of this, nobody can hurt you more either – something which becomes devastatingly clear in The Water Cure.

The psychological element of sister relationships is something that has long fascinated me and other writers. You’re expected to love them - but then you have sibling rivalries, differences in how you’re treated, and more. There’s often an undercurrent of cruelty, even in sibling relationships that seem all sweetness on the surface. And then you have the properly cruel ones. Cinderella, famously tormented by her evil stepsisters; the tragedies in King Lear orchestrated by Goneril and Regan, even as the good sister Cordelia is cast out.

In The Water Cure, cruelty is often encouraged by the parents of Grace, Lia, and Sky, who treat their middle daughter as subtly lesser than her sisters – less deserving of love. And it is this cruelty and subsequent loneliness that drives her to become close to the men who wash up on their island, the only men she has ever known apart from her father, setting everything in motion. I wanted to take these normal sibling rivalries and ask: what would happen if they were put in an environment where the stakes were higher, where jealousy and love could become a matter of life and death?

Sister-sister relationships also lend themselves to an eerie claustrophobia due to their closeness, which can verge on the supernatural. In The Virgin Suicides the world of the sisters is evoked almost unbearably - their clothes scattered everywhere, trinkets and make-up, the girls shut in day after day after day. Even their periods are synchronised, as if they are really one girl. All they have is each other, and their closeness and isolation eventually leads to a devastating conclusion. In We Have Always Lived in the Castle, sisters Merricat and Constance are ostracised by their neighbours, retreating into a claustrophobic world of their own sympathetic magic and rituals. In both these novels, men try either to save the girls or to insinuate themselves into their lives, but they are no match for sisterhood and its power.

I can never talk about sisterhood in fiction without returning to All My Puny Sorrows by Miriam Toews, one of the most complex, honest and heart-rending portrayals of sisterhood I have ever known. It follows two sisters - the older Elfrieda, a world-class concert pianist with a seemingly perfect life - and Yolandi, the scrappier, rodeo-novel writing, younger sister with two divorces under her belt. For all their differences, at the heart of the novel is a core of absolute love between the two sisters: Elfrieda also suffers from severe depression, is in hospital, and wants Yolandi to help her end her life. Throughout the novel we’re confronted with questions about how far you can go for love. Would you go against all your instincts to keep the person you love alive at any cost, when all they want is for you to help them die?

Sisterhood is no light and airy bond; it is existential, raw, one of the most intense forms of love there is. However it is also a source of kindness, of support, of friendship. Re-reading Little Women recently for the first time since childhood, I was struck by the tenderness between them, even during the times they hurt or annoy each other; how, though their differences sometimes make them scornful of each other, they still accept and appreciate each other for who they are.

That is what I wanted to return to, ultimately, in The Water Cure: the idea of sisterhood as a strong and supportive bond, despite everything that happens to the girls. The sisters hurt each other in their own ways, but even the hurting comes from a place of love - a desire to protect, to keep each other safe. And particularly in a post #MeToo world, networks of sisterhood are ever more important; we see more than ever how women supporting women holds power, how this kind of love is a vital driver of change.