This chapter on tree water relations of the Himalayas is based on the trees of three regions with monsoonal precipitation regime: lower elevation forests and also treeline forests of Kumaun, Uttarakhand; and Kathmandu Valley forests, Nepal. The parameters studied were soil Ψ, tree Ψ, osmotic adjustment, and leaf conductance across the seasons. In Kumaun forests, from monsoon to premonsoon, average soil Ψ across all sites decreased by 5.4 times and average tree species ΨPD by 2.75 times. In Kumaun forests, all species, but Shorea robusta, experienced less than −1 MPa ΨPD values, in the treeline, 5 out of the 70 instances were lower than −1 MPa, and in Kathmandu, none of the species showed −1 MPa or less ΨPD. In the monsoon season, ΨPD was highest and ΨΔ lowest in Kumaun trees, while in treeline, both ΨPD and ΨΔ (ΨPD—ΨMD) were the highest. In response to drought, chir pine closed its stomata while ΨPD was still high (isohydric), while oaks kept stomata open up to much lower ΨPD (anisohydric). Broad-leaved evergreen species, including oaks, showed high osmotic adjustment across the species, it was 1.11 at Ψsf and Ψsz in Kumaun and Ψsf 1.30 and Ψsf 1.77 in the treeline. Leaf conductance across all seasons and species was between 60 and 500 m mol m−2 s−1. However, extraordinarily high conductance rate (>1000 mmol m−2 s−1) occurred during autumn in dry Chitkul sites of the Inner Himalayas. Water stored in a wood plays a critical role in leafing and flowering of some of the species of Kathmandu. In brief, in the monsoonal precipitation regime of the Himalayas, water stress is seasonal and mild, but it is enough to cause the dominance of species with sclerophyllous leaves.