Regarding units of water potential and chemical potential
According to German Wikipedia water potential is defined as
$$\psi := \frac{\mu - \mu_0}{\bar{V}},\tag{1}$$
where $\mu_0$ is the standard chemical potential (usually pure water at atmospheric pressure at a specified reference height), and $\bar{V} \approx \pu{18 cm3 mol-1}$ is the molar volume of pure liquid water.
This means that water potential $\psi$ is defined as energy $E$ per volume $V$, which is equivalent to pressure $p$ if you perform dimensional analysis:
$$[\psi] = \frac{[E]}{[V]} = \frac{\mathsf{L}^2·\mathsf{M}·\mathsf{T}^{−2}}{\mathsf{L}^3} = \mathsf{M}·\mathsf{L}^{−1}·\mathsf{T}^{−2} = [p]\tag{2}$$
Megapascal $\pu{MPa}$ is usually used as the unit of measurement; tensiometers are usually graded in hectopascals $\pu{hPa}.$